<!--- 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 -->

"""Mark the package for install."""
        is_newer_version_installed = self._is_newer_version_installed(pkg_spec)
        is_installed = self._is_installed(pkg_spec)
        try:
            if is_newer_version_installed:
                if self.allow_downgrade:
                    
                    
                    
                    
                    if upgrade:
                        if is_installed:
                            self.base.upgrade(pkg_spec)
                        else:
                            self.base.install(pkg_spec)
                    else:
                        self.base.install(pkg_spec)
                else:  
                    pass
            elif is_installed:  
                if upgrade:
                    self.base.upgrade(pkg_spec)
                else:  
                    pass
            else: