<!--- Verify first that your issue is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Explain the problem briefly below -->
We publish semver collection (vyos.vyos:0.0.1-dev58) to ansible galaxy, however by default it seems ansible-galaxy client will not be able to find it. You must specific the version number directly to fetch it.

https://galaxy.ansible.com/vyos/vyos


EDIT:

This is working as expect, but it would be nice to Include:

   --pre                       Include pre-release and development versions. By default, ansible-galaxy only finds stable versions.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
ansible-galaxy

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.9.1
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below

```


##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml
$ ansible-galaxy collection install vyos.vyos -p /tmp/11123
[WARNING]: The specified collections path '/tmp/11123' is not part of the configured Ansible collections paths '/home/pabelanger/.ansible/collections:/usr/share/ansible/collections'. The
installed collection won't be picked up in an Ansible run.

Process install dependency map
ERROR! Cannot meet requirement * for dependency vyos.vyos from source 'https://galaxy.ansible.com/api/'. Available versions before last requirement added: 
Requirements from:
	base - 'vyos.vyos:*'
(venv) [pabelanger@localhost openstack]$ ansible-galaxy collection install vyos.vyos:0.0.1-dev57 -p /tmp/11123
[WARNING]: The specified collections path '/tmp/11123' is not part of the configured Ansible collections paths '/home/pabelanger/.ansible/collections:/usr/share/ansible/collections'. The
installed collection won't be picked up in an Ansible run.

Process install dependency map
Starting collection install process
Installing 'vyos.vyos:0.0.1-dev57' to '/tmp/11123/ansible_collections/vyos/vyos'
```

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->
vyos.vyos collection to be found and installed

##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->

<!--- Paste verbatim command output between quotes -->
```paste below

```

---
            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 file_requirements is None:
            raise AnsibleError("No requirements found in file '%s'" % to_native(requirements_file))
        def parse_role_req(requirement):