<!--- 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 -->

msg="Cache updated",
                    rc=rc,
                    results=[]
                )
            else:
                self.module.exit_json(
                    changed=False,
                    msg="Failed to update cache",
                    rc=rc,
                    results=[stderr],
                )
        repoquerybin = self.module.get_bin_path('repoquery', required=False)
        if self.install_repoquery and not repoquerybin and not self.module.check_mode:
            yum_path = self.module.get_bin_path('yum')
            if yum_path:
                if self.releasever:
                    self.module.run_command('%s -y install yum-utils --releasever %s' % (yum_path, self.releasever))
                else:
                    self.module.run_command('%s -y install yum-utils' % yum_path)
            repoquerybin = self.module.get_bin_path('repoquery', required=False)
        if self.list:
            if not repoquerybin:
                self.module.fail_json(msg="repoquery is required to use list= with this module. Please install the yum-utils package.")
            results = {'results': self.list_stuff(repoquerybin, self.list)}
        else:
            
            
            
            repoquery = None
            try: