<!--- 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 -->

envra = self.local_envra(spec)
                    if envra is None:
                        self.module.fail_json(msg="Failed to get nevra information from RPM package: %s" % spec)
                    
                    if self.is_installed(repoq, envra):
                        pkgs['update'].append(spec)
                    else:
                        pkgs['install'].append(spec)
                    continue
                
                if '://' in spec:
                    
                    with self.set_env_proxy():
                        package = fetch_file(self.module, spec)
                    envra = self.local_envra(package)
                    if envra is None:
                        self.module.fail_json(msg="Failed to get nevra information from RPM package: %s" % spec)
                    
                    if self.is_installed(repoq, envra):
                        pkgs['update'].append(spec)
                    else:
                        pkgs['install'].append(spec)
                    continue
                
                if self.is_installed(repoq, spec):
                    pkgs['update'].append(spec)
                else:
                    pkgs['install'].append(spec)
                pkglist = self.what_provides(repoq, spec)