<!--- 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._update_only(pkgs)
        else:
            for pkg in pkgs:
                try:
                    if self._is_newer_version_installed(self._package_dict(pkg)['nevra']):
                        if self.allow_downgrade:
                            self.base.package_install(pkg)
                    else:
                        self.base.package_install(pkg)
                except Exception as e:
                    self.module.fail_json(
                        msg="Error occured attempting remote rpm operation: {0}".format(to_native(e)),
                        results=[],
                        rc=1,
                    )
    def _is_module_installed(self, module_spec):
        if self.with_modules:
            module_spec = module_spec.strip()
            module_list, nsv = self.module_base._get_modules(module_spec)
            enabled_streams = self.base._moduleContainer.getEnabledStream(nsv.name)
            if enabled_streams:
                if nsv.stream:
                    if nsv.stream in enabled_streams:
                        return True     
                    else:
                        return False    
                else:
                    return True         
        return False  
    def ensure(self):