<!--- Verify first that your feature was not already discussed on GitHub -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Describe the new feature/improvement briefly below -->
Add a --cacheonly option to the ansible yum module, similar to the --downloadonly option.

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
lib/ansible/modules/packaging/os/yum.py

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->
We have a group of Oracle servers that have no repository management server.  They update directly from Oracle's repositories.  Our thought is to do a "yum update --downloadonly" on all dev and prod servers.  Then we can update the dev servers first using "yum update --cacheonly" to test then updated and run the same command on the prod at a later time to make them consistent with the dev.
<!--- Paste example playbooks or commands between quotes below -->
```yaml

```

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

response = {
            'msg': "",
            'changed': False,
            'results': [],
            'rc': 0
        }
        
        
        failure_response = {
            'msg': "",
            'failures': [],
            'results': [],
            'rc': 1
        }
        
        
        if not self.names and self.autoremove:
            self.names = []
            self.state = 'absent'
        if self.names == ['*'] and self.state == 'latest':
            try:
                self.base.upgrade_all()
            except dnf.exceptions.DepsolveError as e:
                failure_response['msg'] = "Depsolve Error occured attempting to upgrade all packages"
                self.module.fail_json(**failure_response)
        else:
            pkg_specs, group_specs, module_specs, filenames = self._parse_spec_group_file()