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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 -->

separated string
    type: list
    elements: str
    version_added: "0.9"
  conf_file:
    description:
      - The remote yum configuration file to use for the transaction.
    type: str
    version_added: "0.6"
  disable_gpg_check:
    description:
      - Whether to disable the GPG checking of signatures of packages being
        installed. Has an effect only if state is I(present) or I(latest).
    type: bool
    default: "no"
    version_added: "1.2"
  skip_broken:
    description:
      - Skip packages with broken dependencies(devsolve) and are causing problems.
    type: bool
    default: "no"
    version_added: "2.3"
  update_cache:
    description:
      - Force yum to check if cache is out of date and redownload if needed.
        Has an effect only if state is I(present) or I(latest).
    type: bool
    default: "no"
    aliases: [ expire-cache ]
    version_added: "1.9"