<!--- 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 -->

continue
            pkg, version, repo = line[0], line[1], line[2]
            name, dist = pkg.rsplit('.', 1)
            if name not in updates:
                updates[name] = []
            updates[name].append({'version': version, 'dist': dist, 'repo': repo})
            if len(line) == 6:
                obsolete_pkg, obsolete_version, obsolete_repo = line[3], line[4], line[5]
                obsolete_name, obsolete_dist = obsolete_pkg.rsplit('.', 1)
                if obsolete_name not in obsoletes:
                    obsoletes[obsolete_name] = []
                obsoletes[obsolete_name].append({'version': obsolete_version, 'dist': obsolete_dist, 'repo': obsolete_repo})
        return updates, obsoletes
    def latest(self, items, repoq):
        res = {}
        res['results'] = []
        res['msg'] = ''
        res['changed'] = False
        res['rc'] = 0
        pkgs = {}
        pkgs['update'] = []
        pkgs['install'] = []
        updates = {}
        obsoletes = {}
        update_all = False
        cmd = None
        
        if '*' in items:
            update_all = True
        rc, out, err = self.run_check_update()