<!--- 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 -->

pkg_specs = [p.strip() for p in pkg_specs]
            filenames = [f.strip() for f in filenames]
            groups = []
            environments = []
            for group_spec in (g.strip() for g in group_specs):
                group = self.base.comps.group_by_pattern(group_spec)
                if group:
                    groups.append(group.id)
                else:
                    environment = self.base.comps.environment_by_pattern(group_spec)
                    if environment:
                        environments.append(environment.id)
                    else:
                        self.module.fail_json(
                            msg="No group {0} available.".format(group_spec),
                            results=[],
                        )
            if self.state in ['installed', 'present']:
                
                self._install_remote_rpms(filenames)
                for filename in filenames:
                    response['results'].append("Installed {0}".format(filename))
                
                if module_specs and self.with_modules:
                    for module in module_specs:
                        try:
                            if not self._is_module_installed(module):
                                response['results'].append("Module {0} installed.".format(module))
                            self.module_base.install([module])
                            self.module_base.enable([module])