##### 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"

existing = [c for c in existing_collections if to_text(c) == to_text(collection_info)]
    if existing and not collection_info.force:
        
        existing[0].add_requirement(to_text(collection_info), requirement)
        collection_info = existing[0]
    dep_map[to_text(collection_info)] = collection_info
def _urljoin(*args):
    return '/'.join(to_native(a, errors='surrogate_or_strict').rstrip('/') for a in args + ('',))
def _download_file(url, b_path, expected_hash, validate_certs):
    bufsize = 65536
    digest = sha256()
    urlsplit = os.path.splitext(to_text(url.rsplit('/', 1)[1]))
    b_file_name = to_bytes(urlsplit[0], errors='surrogate_or_strict')
    b_file_ext = to_bytes(urlsplit[1], errors='surrogate_or_strict')
    b_file_path = tempfile.NamedTemporaryFile(dir=b_path, prefix=b_file_name, suffix=b_file_ext, delete=False).name
    display.vvv("Downloading %s to %s" % (url, to_text(b_path)))
    resp = open_url(to_native(url, errors='surrogate_or_strict'), validate_certs=validate_certs)
    with open(b_file_path, 'wb') as download_file:
        data = resp.read(bufsize)
        while data:
            digest.update(data)
            download_file.write(data)
            data = resp.read(bufsize)
    if expected_hash:
        actual_hash = digest.hexdigest()
        display.vvvv("Validating downloaded file hash %s with expected hash %s" % (actual_hash, expected_hash))
        if expected_hash != actual_hash:
            raise AnsibleError("Mismatch artifact hash with downloaded file")
    return b_file_path
def _extract_tar_file(tar, filename, b_dest, b_temp_path, expected_hash=None):