##### 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"

:return: A list of tuples (name, version, source).
    """
    collection_info = []
    b_requirements_file = to_bytes(requirements_file, errors='surrogate_or_strict')
    if not os.path.exists(b_requirements_file):
        raise AnsibleError("The requirements file '%s' does not exist." % to_native(requirements_file))
    display.vvv("Reading collection requirement file at '%s'" % requirements_file)
    with open(b_requirements_file, 'rb') as req_obj:
        try:
            requirements = yaml.safe_load(req_obj)
        except YAMLError as err:
            raise AnsibleError("Failed to parse the collection requirements yml at '%s' with the following error:\n%s"
                               % (to_native(requirements_file), to_native(err)))
    if not isinstance(requirements, dict) or 'collections' not in requirements:
        
        raise AnsibleError("Expecting collections requirements file to be a dict with the key "
                           "collections that contains a list of collections to install.")
    for collection_req in requirements['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)
            collection_info.append((req_name, req_version, req_source))
        else:
            collection_info.append((collection_req, '*', None))
    return collection_info
@contextmanager
def _tempdir():