<!--- 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 -->

self.module = module
        self.allow_downgrade = self.module.params['allow_downgrade']
        self.autoremove = self.module.params['autoremove']
        self.bugfix = self.module.params['bugfix']
        self.conf_file = self.module.params['conf_file']
        self.disable_excludes = self.module.params['disable_excludes']
        self.disable_gpg_check = self.module.params['disable_gpg_check']
        self.disable_plugin = self.module.params['disable_plugin']
        self.disablerepo = self.module.params.get('disablerepo', [])
        self.download_only = self.module.params['download_only']
        self.download_dir = self.module.params['download_dir']
        self.enable_plugin = self.module.params['enable_plugin']
        self.enablerepo = self.module.params.get('enablerepo', [])
        self.exclude = self.module.params['exclude']
        self.installroot = self.module.params['installroot']
        self.install_repoquery = self.module.params['install_repoquery']
        self.install_weak_deps = self.module.params['install_weak_deps']
        self.list = self.module.params['list']
        self.names = [p.strip() for p in self.module.params['name']]
        self.releasever = self.module.params['releasever']
        self.security = self.module.params['security']
        self.skip_broken = self.module.params['skip_broken']
        self.state = self.module.params['state']
        self.update_only = self.module.params['update_only']
        self.update_cache = self.module.params['update_cache']
        self.validate_certs = self.module.params['validate_certs']
        self.lock_timeout = self.module.params['lock_timeout']