<!--- 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 AttributeError:
            pass  
        try:
            if self.update_cache:
                try:
                    base.update_cache()
                except dnf.exceptions.RepoError as e:
                    self.module.fail_json(
                        msg="{0}".format(to_text(e)),
                        results=[],
                        rc=1
                    )
            base.fill_sack(load_system_repo='auto')
        except dnf.exceptions.RepoError as e:
            self.module.fail_json(
                msg="{0}".format(to_text(e)),
                results=[],
                rc=1
            )
        filters = []
        if self.bugfix:
            key = {'advisory_type__eq': 'bugfix'}
            filters.append(base.sack.query().upgrades().filter(**key))
        if self.security:
            key = {'advisory_type__eq': 'security'}
            filters.append(base.sack.query().upgrades().filter(**key))
        if filters:
            base._update_security_filters = filters
        return base
    def list_items(self, command):