<!--- 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 -->

if pkgstr.strip() and pkgstr.count('|') == 5:
            n, e, v, r, a, repo = pkgstr.split('|')
        else:
            return {'error_parsing': pkgstr}
        d = {
            'name': n,
            'arch': a,
            'epoch': e,
            'release': r,
            'version': v,
            'repo': repo,
            'envra': '%s:%s-%s-%s.%s' % (e, n, v, r, a)
        }
        if repo == 'installed':
            d['yumstate'] = 'installed'
        else:
            d['yumstate'] = 'available'
        return d
    def repolist(self, repoq, qf="%{repoid}"):
        cmd = repoq + ["--qf", qf, "-a"]
        if self.releasever:
            cmd.extend(['--releasever=%s' % self.releasever])
        rc, out, _ = self.module.run_command(cmd)
        if rc == 0:
            return set(p for p in out.split('\n') if p.strip())
        else:
            return []
    def list_stuff(self, repoquerybin, stuff):