##### 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)]
```

---
            roles:
            # Same as v1 format just under the roles key
            collections:
            - namespace.collection
            - name: namespace.collection
              version: version identifier, multiple identifiers are separated by ','
              source: the URL or a predefined source name that relates to C.GALAXY_SERVER_LIST
        :param requirements_file: The path to the requirements file.
        :param allow_old_format: Will fail if a v1 requirements file is found and this is set to False.
        :return: a dict containing roles and collections to found in the requirements file.
        """
        requirements = {
            'roles': [],
            'collections': [],
        }
        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 requirement file at '%s'" % requirements_file)
        with open(b_requirements_file, 'rb') as req_obj:
            try:
                file_requirements = yaml.safe_load(req_obj)
            except YAMLError as err:
                raise AnsibleError(
                    "Failed to parse the requirements yml at '%s' with the following error:\n%s"
                    % (to_native(requirements_file), to_native(err)))
        if requirements_file is None:
            raise AnsibleError("No requirements found in file '%s'" % to_native(requirements_file))
        def parse_role_req(requirement):