<!--- Verify first that your feature was not already discussed on GitHub -->
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##### 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 -->

- This setting affects packages installed from a repository as well as
        "local" packages installed from the filesystem or a URL.
    type: bool
    default: 'no'
  installroot:
    description:
      - Specifies an alternative installroot, relative to which all packages
        will be installed.
    version_added: "2.3"
    default: "/"
    type: str
  releasever:
    description:
      - Specifies an alternative release from which all packages will be
        installed.
    version_added: "2.6"
    type: str
  autoremove:
    description:
      - If C(yes), removes all "leaf" packages from the system that were originally
        installed as dependencies of user-installed packages but which are no longer
        required by any such package. Should be used alone or when state is I(absent)
    type: bool
    default: "no"
    version_added: "2.4"
  exclude:
    description:
      - Package name(s) to exclude when state=present, or latest. This can be a
        list or a comma separated string.
    version_added: "2.7"