<!--- 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 = []
        downgrade_pkgs = []
        res = {}
        res['results'] = []
        res['msg'] = ''
        res['rc'] = 0
        res['changed'] = False
        for spec in items:
            pkg = None
            downgrade_candidate = False
            
            if spec.endswith('.rpm') or '://' in spec:
                if '://' not in spec and not os.path.exists(spec):
                    res['msg'] += "No RPM file matching '%s' found on system" % spec
                    res['results'].append("No RPM file matching '%s' found on system" % spec)
                    res['rc'] = 127  
                    self.module.fail_json(**res)
                if '://' in spec:
                    with self.set_env_proxy():
                        package = fetch_file(self.module, spec)
                        if not package.endswith('.rpm'):
                            
                            
                            new_package_path = '%s.rpm' % package
                            os.rename(package, new_package_path)