##### SUMMARY
As a nicety to the user, `ansible-galaxy collection` should check certain properties of the `collection_name` argument, and provide helpful suggestions about expected format.

##### ISSUE TYPE
- Feature Idea

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

##### ADDITIONAL INFORMATION
When getting this message, it's not clear to the user what they should do differently:

```yaml
$ ansible-galaxy collection install chrismeyersfsu_tower_modules -p alan -vvv
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
Opened /Users/alancoding/.ansible_galaxy
 [WARNING]: The specified collections path '/Users/alancoding/Documents/repos/jlaska-ansible-playbooks/alan' is not part of the configured Ansible collections paths
'/Users/alancoding/.ansible/collections:/usr/share/ansible/collections'. The installed collection won't be picked up in an Ansible run.

Found installed collection chrismeyersfsu.tower_modules:0.0.1 at '/Users/alancoding/Documents/repos/jlaska-ansible-playbooks/alan/ansible_collections/chrismeyersfsu/tower_modules'
Processing requirement collection 'chrismeyersfsu_tower_modules'
ERROR! Unexpected Exception, this is probably a bug: not enough values to unpack (expected 2, got 1)
the full traceback was:

Traceback (most recent call last):
  File "/Users/alancoding/Documents/repos/ansible/bin/ansible-galaxy", line 111, in <module>
    exit_code = cli.run()
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/cli/galaxy.py", line 269, in run
    context.CLIARGS['func']()
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/cli/galaxy.py", line 617, in execute_install
    no_deps, force, force_deps)
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/galaxy/collection.py", line 450, in install_collections
    force, force_deps, no_deps)
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/galaxy/collection.py", line 831, in _build_dependency_map
    validate_certs, (force or force_deps))
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/galaxy/collection.py", line 898, in _get_collection_info
    parent=parent)
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/galaxy/collection.py", line 296, in from_name
    namespace, name = collection.split('.', 1)
ValueError: not enough values to unpack (expected 2, got 1)
```

Instead of `ValueError`, it would be better to give text like

> Improperly formatted collection name argument. Collection name must be of the format "username.collection_name", like "chrismeyersfsu.tower_modules"

mock_install, mock_warning, output_dir = collection_install
    requirements_file = os.path.join(output_dir, 'requirements.yml')
    with open(requirements_file, 'wb') as req_obj:
        req_obj.write(b'''---
collections:
- namespace.coll
- name: namespace2.coll
  version: '>2.0.1'
''')
    galaxy_args = ['ansible-galaxy', 'collection', 'install', '--requirements-file', requirements_file,
                   '--collections-path', output_dir]
    GalaxyCLI(args=galaxy_args).run()
    collection_path = os.path.join(output_dir, 'ansible_collections')
    assert os.path.isdir(collection_path)
    assert mock_warning.call_count == 1
    assert "The specified collections path '%s' is not part of the configured Ansible collections path" % output_dir \
        in mock_warning.call_args[0][0]
    assert mock_install.call_count == 1
    assert mock_install.call_args[0][0] == [('namespace.coll', '*', None),
                                            ('namespace2.coll', '>2.0.1', None)]
    assert mock_install.call_args[0][1] == collection_path
    assert mock_install.call_args[0][2] == ['https://galaxy.ansible.com']
    assert mock_install.call_args[0][3] is True
    assert mock_install.call_args[0][4] is False
    assert mock_install.call_args[0][5] is False
    assert mock_install.call_args[0][6] is False
    assert mock_install.call_args[0][7] is False
def test_collection_install_with_relative_path(collection_install, monkeypatch):