##### 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"

collection = type_parser.add_parser('collection',
                                            parents=[common],
                                            help='Manage an Ansible Galaxy collection.')
        collection_parser = collection.add_subparsers(metavar='ACTION', dest='collection')
        collection_parser.required = True
        build_parser = collection_parser.add_parser(
            'build', help='Build an Ansible collection artifact that can be published to Ansible Galaxy.',
            parents=[common, force])
        build_parser.set_defaults(func=self.execute_build)
        build_parser.add_argument(
            'args', metavar='collection', nargs='*', default=('./',),
            help='Path to the collection(s) directory to build. This should be the directory that contains the '
                 'galaxy.yml file. The default is the current working directory.')
        build_parser.add_argument(
            '--output-path', dest='output_path', default='./',
            help='The path in which the collection is built to. The default is the current working directory.')
        self.add_init_parser(collection_parser, [common, force])
        cinstall_parser = collection_parser.add_parser('install', help='Install collection from Ansible Galaxy',
                                                       parents=[force, common])
        cinstall_parser.set_defaults(func=self.execute_install)
        cinstall_parser.add_argument('args', metavar='collection_name', nargs='*',
                                     help='The collection(s) name or path/url to a tar.gz collection artifact. This '
                                          'is mutually exclusive with --requirements-file.')
        cinstall_parser.add_argument('-p', '--collections-path', dest='collections_path', required=True,
                                     help='The path to the directory containing your collections.')
        cinstall_parser.add_argument('-i', '--ignore-errors', dest='ignore_errors', action='store_true', default=False,
                                     help='Ignore errors during installation and continue with the next specified '
                                          'collection. This will not ignore dependency conflict errors.')
        cinstall_parser.add_argument('-r', '--requirements-file', dest='requirements',
                                     help='A file containing a list of collections to be installed.')