##### 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"

from ansible.utils.hashing import secure_hash, secure_hash_s
from ansible.module_utils.urls import open_url
urlparse = six.moves.urllib.parse.urlparse
urllib_error = six.moves.urllib.error
display = Display()
MANIFEST_FORMAT = 1
class CollectionRequirement:
    _FILE_MAPPING = [(b'MANIFEST.json', 'manifest_file'), (b'FILES.json', 'files_file')]
    def __init__(self, namespace, name, b_path, source, versions, requirement, force, parent=None, validate_certs=True,
                 metadata=None, files=None, skip=False):
        """
        Represents a collection requirement, the versions that are available to be installed as well as any
        dependencies the collection has.
        :param namespace: The collection namespace.
        :param name: The collection name.
        :param b_path: Byte str of the path to the collection tarball if it has already been downloaded.
        :param source: The Galaxy server URL to download if the collection is from Galaxy.
        :param versions: A list of versions of the collection that are available.
        :param requirement: The version requirement string used to verify the list of versions fit the requirements.
        :param force: Whether the force flag applied to the collection.
        :param parent: The name of the parent the collection is a dependency of.
        :param validate_certs: Whether to validate the Galaxy server certificate.
        :param metadata: The collection metadata dict if it has already been retrieved.
        :param files: The files that exist inside the collection. This is based on the FILES.json file inside the
            collection artifact.
        :param skip: Whether to skip installing the collection. Should be set if the collection is already installed
            and force is not set.
        """
        self.namespace = namespace
        self.name = name