##### 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"

display.warning(u"- %s was NOT installed successfully: %s " % (role.name, to_text(e)))
                self.exit_without_ignore()
                continue
            
            if not no_deps and installed:
                if not role.metadata:
                    display.warning("Meta file %s is empty. Skipping dependencies." % role.path)
                else:
                    role_dependencies = role.metadata.get('dependencies') or []
                    for dep in role_dependencies:
                        display.debug('Installing dep %s' % dep)
                        dep_req = RoleRequirement()
                        dep_info = dep_req.role_yaml_parse(dep)
                        dep_role = GalaxyRole(self.galaxy, **dep_info)
                        if '.' not in dep_role.name and '.' not in dep_role.src and dep_role.scm is None:
                            
                            
                            continue
                        if dep_role.install_info is None:
                            if dep_role not in roles_left:
                                display.display('- adding dependency: %s' % to_text(dep_role))
                                roles_left.append(dep_role)
                            else:
                                display.display('- dependency %s already pending installation.' % dep_role.name)
                        else:
                            if dep_role.install_info['version'] != dep_role.version:
                                if force_deps:
                                    display.display('- changing dependant role %s from %s to %s' %
                                                    (dep_role.name, dep_role.install_info['version'], dep_role.version or "unspecified"))
                                    dep_role.remove()