<!--- 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 -->

break
        return conflicts
    def local_envra(self, path):
        """return envra of a local rpm passed in"""
        ts = rpm.TransactionSet()
        ts.setVSFlags(rpm._RPMVSF_NOSIGNATURES)
        fd = os.open(path, os.O_RDONLY)
        try:
            header = ts.hdrFromFdno(fd)
        except rpm.error as e:
            return None
        finally:
            os.close(fd)
        return '%s:%s-%s-%s.%s' % (
            header[rpm.RPMTAG_EPOCH] or '0',
            header[rpm.RPMTAG_NAME],
            header[rpm.RPMTAG_VERSION],
            header[rpm.RPMTAG_RELEASE],
            header[rpm.RPMTAG_ARCH]
        )
    @contextmanager
    def set_env_proxy(self):
        
        namepass = ""
        scheme = ["http", "https"]
        old_proxy_env = [os.getenv("http_proxy"), os.getenv("https_proxy")]
        try:
            
            if self.yum_base.conf.proxy and self.yum_base.conf.proxy not in ("_none_",):
                if self.yum_base.conf.proxy_username: