<!--- 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 -->

if compare > 0 and self.allow_downgrade:
                        downgrade_candidate = True
                    elif compare >= 0:
                        continue
                
                
                pkg = package
            
            elif spec.startswith('@'):
                if self.is_group_env_installed(spec):
                    continue
                pkg = spec
            
            else:
                
                
                
                if not set(['*', '?']).intersection(set(spec)):
                    installed_pkgs = self.is_installed(repoq, spec, is_pkg=True)
                    if installed_pkgs:
                        res['results'].append('%s providing %s is already installed' % (installed_pkgs[0], spec))
                        continue
                
                pkglist = self.what_provides(repoq, spec)
                if not pkglist:
                    res['msg'] += "No package matching '%s' found available, installed or updated" % spec
                    res['results'].append("No package matching '%s' found available, installed or updated" % spec)
                    res['rc'] = 126