<!--- Verify first that your issue is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Explain the problem briefly below -->
We publish semver collection (vyos.vyos:0.0.1-dev58) to ansible galaxy, however by default it seems ansible-galaxy client will not be able to find it. You must specific the version number directly to fetch it.

https://galaxy.ansible.com/vyos/vyos


EDIT:

This is working as expect, but it would be nice to Include:

   --pre                       Include pre-release and development versions. By default, ansible-galaxy only finds stable versions.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
ansible-galaxy

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.9.1
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below

```


##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml
$ ansible-galaxy collection install vyos.vyos -p /tmp/11123
[WARNING]: The specified collections path '/tmp/11123' is not part of the configured Ansible collections paths '/home/pabelanger/.ansible/collections:/usr/share/ansible/collections'. The
installed collection won't be picked up in an Ansible run.

Process install dependency map
ERROR! Cannot meet requirement * for dependency vyos.vyos from source 'https://galaxy.ansible.com/api/'. Available versions before last requirement added: 
Requirements from:
	base - 'vyos.vyos:*'
(venv) [pabelanger@localhost openstack]$ ansible-galaxy collection install vyos.vyos:0.0.1-dev57 -p /tmp/11123
[WARNING]: The specified collections path '/tmp/11123' is not part of the configured Ansible collections paths '/home/pabelanger/.ansible/collections:/usr/share/ansible/collections'. The
installed collection won't be picked up in an Ansible run.

Process install dependency map
Starting collection install process
Installing 'vyos.vyos:0.0.1-dev57' to '/tmp/11123/ansible_collections/vyos/vyos'
```

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->
vyos.vyos collection to be found and installed

##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->

<!--- Paste verbatim command output between quotes -->
```paste below

```

raise AnsibleError("Expecting requirements file to be a dict with the key 'collections' that contains "
                                   "a list of collections to install")
            for role_req in file_requirements:
                requirements['roles'] += parse_role_req(role_req)
        else:
            
            extra_keys = set(file_requirements.keys()).difference(set(['roles', 'collections']))
            if extra_keys:
                raise AnsibleError("Expecting only 'roles' and/or 'collections' as base keys in the requirements "
                                   "file. Found: %s" % (to_native(", ".join(extra_keys))))
            for role_req in file_requirements.get('roles', []):
                requirements['roles'] += parse_role_req(role_req)
            for collection_req in file_requirements.get('collections', []):
                if isinstance(collection_req, dict):
                    req_name = collection_req.get('name', None)
                    if req_name is None:
                        raise AnsibleError("Collections requirement entry should contain the key name.")
                    req_version = collection_req.get('version', '*')
                    req_source = collection_req.get('source', None)
                    if req_source:
                        
                        
                        req_source = next(iter([a for a in self.api_servers if req_source in [a.name, a.api_server]]),
                                          GalaxyAPI(self.galaxy, "explicit_requirement_%s" % req_name, req_source))
                    requirements['collections'].append((req_name, req_version, req_source))
                else:
                    requirements['collections'].append((collection_req, '*', None))
        return requirements
    @staticmethod
    def exit_without_ignore(rc=1):