<!--- 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 -->

except dnf.exceptions.MarkingErrors as e:
                            failure_response['failures'].append(' '.join((module, to_native(e))))
                for group in groups:
                    try:
                        self.base.group_remove(group)
                    except dnf.exceptions.CompsError:
                        
                        pass
                    except AttributeError:
                        
                        
                        #
                        
                        
                        
                        pass
                for environment in environments:
                    try:
                        self.base.environment_remove(environment)
                    except dnf.exceptions.CompsError:
                        
                        pass
                installed = self.base.sack.query().installed()
                for pkg_spec in pkg_specs:
                    
                    if '*' in pkg_spec:
                        try:
                            self.base.remove(pkg_spec)
                        except dnf.exceptions.MarkingError as e:
                            is_failure, handled_remove_error = self._sanitize_dnf_error_msg_remove(pkg_spec, to_native(e))