<!--- 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 -->

os.unlink(self.lockfile)
                    return False
            except IOError:
                
                try:
                    
                    os.kill(oldpid, 0)
                except OSError as e:
                    if e.errno == errno.ESRCH:
                        
                        os.unlink(self.lockfile)
                        return False
                    self.module.fail_json(msg="Unable to check PID %s in  %s: %s" % (oldpid, self.lockfile, to_native(e)))
        except (IOError, OSError) as e:
            
            return False
        
        return True
    @property
    def yum_base(self):
        if self._yum_base:
            return self._yum_base
        else:
            
            self._yum_base = yum.YumBase()
            self._yum_base.preconf.debuglevel = 0
            self._yum_base.preconf.errorlevel = 0
            self._yum_base.preconf.plugins = True
            self._yum_base.preconf.enabled_plugins = self.enable_plugin
            self._yum_base.preconf.disabled_plugins = self.disable_plugin