##### SUMMARY
`ansible-galaxy collection install` currently requires the user to specify an install path using the `-p` option. Galaxy currently generates and displays the CLI command for installing a collection. There is no way for Galaxy to determine a value for `-p`, and hard coding a default value into Galaxy makes no sense.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
`ansible-galaxy`

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```
ansible 2.10.0.dev0
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/Users/chouseknecht/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /Users/chouseknecht/projects/ansible/lib/ansible
  executable location = /Users/chouseknecht/.pyenv/versions/venv27/bin/ansible
  python version = 2.7.14 (default, Nov 14 2017, 23:24:24) [GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.38)]
```

requirements = []
                for collection_input in collections:
                    name, dummy, requirement = collection_input.partition(':')
                    requirements.append((name, requirement or '*', None))
            output_path = GalaxyCLI._resolve_path(output_path)
            collections_path = C.COLLECTIONS_PATHS
            if len([p for p in collections_path if p.startswith(output_path)]) == 0:
                display.warning("The specified collections path '%s' is not part of the configured Ansible "
                                "collections paths '%s'. The installed collection won't be picked up in an Ansible "
                                "run." % (to_text(output_path), to_text(":".join(collections_path))))
            if os.path.split(output_path)[1] != 'ansible_collections':
                output_path = os.path.join(output_path, 'ansible_collections')
            b_output_path = to_bytes(output_path, errors='surrogate_or_strict')
            if not os.path.exists(b_output_path):
                os.makedirs(b_output_path)
            install_collections(requirements, output_path, self.api_servers, (not ignore_certs), ignore_errors,
                                no_deps, force, force_deps)
            return 0
        role_file = context.CLIARGS['role_file']
        if not context.CLIARGS['args'] and role_file is None:
            
            raise AnsibleOptionsError("- you must specify a user/role name or a roles file")
        no_deps = context.CLIARGS['no_deps']
        force_deps = context.CLIARGS['force_with_deps']
        force = context.CLIARGS['force'] or force_deps
        roles_left = []
        if role_file:
            if not (role_file.endswith('.yaml') or role_file.endswith('.yml')):
                raise AnsibleError("Invalid role requirements file, it must end with a .yml or .yaml extension")
            roles_left = self._parse_requirements_file(role_file)['roles']