<!--- 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 -->

if hasattr(po, 'ui_envra'):
            return po.ui_envra
        return '%s:%s-%s-%s.%s' % (po.epoch, po.name, po.version, po.release, po.arch)
    def is_group_env_installed(self, name):
        name_lower = name.lower()
        if yum.__version_info__ >= (3, 4):
            groups_list = self.yum_base.doGroupLists(return_evgrps=True)
        else:
            groups_list = self.yum_base.doGroupLists()
        
        groups = groups_list[0]
        for group in groups:
            if name_lower.endswith(group.name.lower()) or name_lower.endswith(group.groupid.lower()):
                return True
        if yum.__version_info__ >= (3, 4):
            
            envs = groups_list[2]
            for env in envs:
                if name_lower.endswith(env.name.lower()) or name_lower.endswith(env.environmentid.lower()):
                    return True
        return False
    def is_installed(self, repoq, pkgspec, qf=None, is_pkg=False):