##### 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"

tarinfo.mode = 0o0755 if tarinfo.isdir() else 0o0644
                    tarinfo.uid = tarinfo.gid = 0
                    tarinfo.uname = tarinfo.gname = ''
                    return tarinfo
                tar_file.add(os.path.realpath(b_src_path), arcname=filename, recursive=False, filter=reset_stat)
        shutil.copy(b_tar_filepath, b_tar_path)
        collection_name = "%s.%s" % (collection_manifest['collection_info']['namespace'],
                                     collection_manifest['collection_info']['name'])
        display.display('Created collection for %s at %s' % (collection_name, to_text(b_tar_path)))
def _get_mime_data(b_collection_path):
    with open(b_collection_path, 'rb') as collection_tar:
        data = collection_tar.read()
    boundary = '--------------------------%s' % uuid.uuid4().hex
    b_file_name = os.path.basename(b_collection_path)
    part_boundary = b"--" + to_bytes(boundary, errors='surrogate_or_strict')
    form = [
        part_boundary,
        b"Content-Disposition: form-data; name=\"sha256\"",
        to_bytes(secure_hash_s(data), errors='surrogate_or_strict'),
        part_boundary,
        b"Content-Disposition: file; name=\"file\"; filename=\"%s\"" % b_file_name,
        b"Content-Type: application/octet-stream",
        b"",
        data,
        b"%s--" % part_boundary,
    ]
    content_type = 'multipart/form-data; boundary=%s' % boundary
    return b"\r\n".join(form), content_type
def _wait_import(task_url, key, validate_certs):