##### SUMMARY
The documentation mentions the ability to specify a galaxy server parameter via the syntax `ANSIBLE_GALAXY_SERVER_{{ id }}_{{ key }}`, but this seems to not be working for the URL of an example of this.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
lib/ansible/cli/galaxy.py

##### ANSIBLE VERSION
```
ansible --version
ansible 2.9.0.dev0
  config file = None
  configured module search path = ['/Users/alancoding/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /Users/alancoding/Documents/repos/ansible/lib/ansible
  executable location = /Users/alancoding/.virtualenvs/ansible3/bin/ansible
  python version = 3.6.5 (default, Apr 25 2018, 14:23:58) [GCC 4.2.1 Compatible Apple LLVM 9.1.0 (clang-902.0.39.1)]
```

##### CONFIGURATION
```
ANSIBLE_NOCOWS(env: ANSIBLE_NOCOWS) = True
```

##### OS / ENVIRONMENT
Mac OS, control machine, also on CentOS


##### STEPS TO REPRODUCE
Run this command

```yaml
ANSIBLE_GALAXY_SERVER_GALAXY_URL=https://galaxy.ansible.com ANSIBLE_GALAXY_SERVER_PRIVATE_GALAXY_URL=https://galaxy-dev.ansible.com ANSIBLE_GALAXY_SERVER_LIST=private_galaxy,galaxy ansible-galaxy collection install -r fallback_not_found/collections/requirements.yml -p dest -vvvv
```

where the content is

```
cat fallback_not_found/collections/requirements.yml
collections:
  - name: "chrismeyersfsu.test_things"
  - name: "chrismeyersfsu.tower_modules"
```

##### EXPECTED RESULTS
I expect it to attempt to install from the development galaxy server, and then get a 404, and then install from the release galaxy server.

This works if I do not use these environment variables and instead use the config:

```
[galaxy]
server_list = dev_galaxy,galaxy

[galaxy_server.dev_galaxy]
url=https://galaxy-dev.ansible.com

[galaxy_server.galaxy]
url=https://galaxy.ansible.com/
```

The documentation describes this use case here:

https://github.com/jborean93/ansible/blob/devel/docs/docsite/rst/dev_guide/collections_tech_preview.rst

> As well as being defined in the ansible.cfg file, these server options can be defined as an environment variable. The environment variable is in the form ANSIBLE_GALAXY_SERVER_{{ id }}_{{ key }} where {{ id }} is the upper case form of the server identifier and {{ key }} is the key to define. For example I can define token for release_galaxy by setting ANSIBLE_GALAXY_SERVER_RELEASE_GALAXY_TOKEN=secret_token.

The setting for the host is `url`

> url: The URL of the galaxy instance to connect to, this is required.

##### ACTUAL RESULTS
```
ansible-galaxy 2.9.0.dev0
  config file = None
  configured module search path = ['/Users/alancoding/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /Users/alancoding/Documents/repos/ansible/lib/ansible
  executable location = /Users/alancoding/.virtualenvs/ansible3/bin/ansible-galaxy
  python version = 3.6.5 (default, Apr 25 2018, 14:23:58) [GCC 4.2.1 Compatible Apple LLVM 9.1.0 (clang-902.0.39.1)]
No config file found; using defaults
ERROR! No setting was provided for required configuration plugin_type: galaxy_server plugin: private_galaxy setting: url 
```

I also tried removing "galaxy" from the names, and this has the same result.

```
ANSIBLE_GALAXY_SERVER_FOO_URL=https://galaxy.ansible.com ANSIBLE_GALAXY_SERVER_BAR_URL=https://galaxy-dev.ansible.com ANSIBLE_GALAXY_SERVER_LIST=bar,foo ansible-galaxy collection install -r fallback_not_found/collections/requirements.yml -p dest -vvvv
ansible-galaxy 2.9.0.dev0
  config file = None
  configured module search path = ['/Users/alancoding/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /Users/alancoding/Documents/repos/ansible/lib/ansible
  executable location = /Users/alancoding/.virtualenvs/ansible3/bin/ansible-galaxy
  python version = 3.6.5 (default, Apr 25 2018, 14:23:58) [GCC 4.2.1 Compatible Apple LLVM 9.1.0 (clang-902.0.39.1)]
No config file found; using defaults
ERROR! No setting was provided for required configuration plugin_type: galaxy_server plugin: bar setting: url 
```

Ping @jborean93 @chrismeyersfsu @ryanpetrello 

We do _not_ rate this as a Tower blocker, because the `ansible.cfg` specification of parameters is known to work, and we will begin to design around that.
display.display("WARNING: More than one Galaxy role associated with Github repo %s/%s." % (github_user, github_repo),
                                color='yellow')
                display.display("The following Galaxy roles are being updated:" + u'\n', color=C.COLOR_CHANGED)
                for t in task:
                    display.display('%s.%s' % (t['summary_fields']['role']['namespace'], t['summary_fields']['role']['name']), color=C.COLOR_CHANGED)
                display.display(u'\nTo properly namespace this role, remove each of the above and re-import %s/%s from scratch' % (github_user, github_repo),
                                color=C.COLOR_CHANGED)
                return 0
            
            display.display("Successfully submitted import request %d" % task[0]['id'])
            if not context.CLIARGS['wait']:
                display.display("Role name: %s" % task[0]['summary_fields']['role']['name'])
                display.display("Repo: %s/%s" % (task[0]['github_user'], task[0]['github_repo']))
        if context.CLIARGS['check_status'] or context.CLIARGS['wait']:
            
            msg_list = []
            finished = False
            while not finished:
                task = self.api.get_import_task(task_id=task[0]['id'])
                for msg in task[0]['summary_fields']['task_messages']:
                    if msg['id'] not in msg_list:
                        display.display(msg['message_text'], color=colors[msg['message_type']])
                        msg_list.append(msg['id'])
                if task[0]['state'] in ['SUCCESS', 'FAILED']:
                    finished = True
                else:
                    time.sleep(10)
        return 0
    def execute_setup(self):