<!--- 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 -->

pkgs = []
        res = {}
        res['results'] = []
        res['msg'] = ''
        res['changed'] = False
        res['rc'] = 0
        for pkg in items:
            if pkg.startswith('@'):
                installed = self.is_group_env_installed(pkg)
            else:
                installed = self.is_installed(repoq, pkg)
            if installed:
                pkgs.append(pkg)
            else:
                res['results'].append('%s is not installed' % pkg)
        if pkgs:
            if self.module.check_mode:
                self.module.exit_json(changed=True, results=res['results'], changes=dict(removed=pkgs))
            else:
                res['changes'] = dict(removed=pkgs)
            
            if self.autoremove:
                cmd = self.yum_basecmd + ["autoremove"] + pkgs
            else: