<!--- 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.fail_json(**res)
                
                
                conflicts = self.transaction_exists(pkglist)
                if conflicts:
                    res['msg'] += "The following packages have pending transactions: %s" % ", ".join(conflicts)
                    res['rc'] = 125  
                    self.module.fail_json(**res)
                
                
                found = False
                for this in pkglist:
                    if self.is_installed(repoq, this, is_pkg=True):
                        found = True
                        res['results'].append('%s providing %s is already installed' % (this, spec))
                        break
                
                
                
                
                
                if not found:
                    if self.is_installed(repoq, spec):
                        found = True
                        res['results'].append('package providing %s is already installed' % (spec))
                if found:
                    continue