##### 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"

remove_parser.set_defaults(func=self.execute_remove)
        remove_parser.add_argument('args', help='Role(s)', metavar='role', nargs='+')
        list_parser = role_parser.add_parser('list', help='Show the name and version of each role installed in the roles_path.',
                                             parents=[common, roles_path])
        list_parser.set_defaults(func=self.execute_list)
        list_parser.add_argument('role', help='Role', nargs='?', metavar='role')
        login_parser = role_parser.add_parser('login', parents=[common],
                                              help="Login to api.github.com server in order to use ansible-galaxy role "
                                                   "sub command such as 'import', 'delete', 'publish', and 'setup'")
        login_parser.set_defaults(func=self.execute_login)
        login_parser.add_argument('--github-token', dest='token', default=None,
                                  help='Identify with github token rather than username and password.')
        search_parser = role_parser.add_parser('search', help='Search the Galaxy database by tags, platforms, author and multiple keywords.',
                                               parents=[common])
        search_parser.set_defaults(func=self.execute_search)
        search_parser.add_argument('--platforms', dest='platforms', help='list of OS platforms to filter by')
        search_parser.add_argument('--galaxy-tags', dest='galaxy_tags', help='list of galaxy tags to filter by')
        search_parser.add_argument('--author', dest='author', help='GitHub username')
        search_parser.add_argument('args', help='Search terms', metavar='searchterm', nargs='*')
        setup_parser = role_parser.add_parser('setup', help='Manage the integration between Galaxy and the given source.',
                                              parents=[roles_path, common])
        setup_parser.set_defaults(func=self.execute_setup)
        setup_parser.add_argument('--remove', dest='remove_id', default=None,
                                  help='Remove the integration matching the provided ID value. Use --list to see ID values.')
        setup_parser.add_argument('--list', dest="setup_list", action='store_true', default=False, help='List all of your integrations.')
        setup_parser.add_argument('source', help='Source')
        setup_parser.add_argument('github_user', help='GitHub username')
        setup_parser.add_argument('github_repo', help='GitHub repository')
        setup_parser.add_argument('secret', help='Secret')
    def add_init_parser(self, parser, parents):