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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 -->

bugfix:
    description:
      - If set to C(yes), and C(state=latest) then only installs updates that have been marked bugfix related.
      - Note that, similar to ``dnf upgrade-minimal``, this filter applies to dependencies as well.
    default: "no"
    type: bool
    version_added: "2.7"
  enable_plugin:
    description:
      - I(Plugin) name to enable for the install/update operation.
        The enabled plugin will not persist beyond the transaction.
    version_added: "2.7"
    type: list
    elements: str
  disable_plugin:
    description:
      - I(Plugin) name to disable for the install/update operation.
        The disabled plugins will not persist beyond the transaction.
    version_added: "2.7"
    type: list
    elements: str
  disable_excludes:
    description:
      - Disable the excludes defined in DNF config files.
      - If set to C(all), disables all excludes.
      - If set to C(main), disable excludes defined in [main] in dnf.conf.
      - If set to C(repoid), disable excludes defined for given repo id.
    version_added: "2.7"
    type: str
  validate_certs: