<!--- 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 -->

name: /usr/local/src/nginx-release-centos-6-0.el6.ngx.noarch.rpm
    state: present
- name: Install the 'Development tools' package group
  yum:
    name: "@Development tools"
    state: present
- name: Install the 'Gnome desktop' environment group
  yum:
    name: "@^gnome-desktop-environment"
    state: present
- name: List ansible packages and register result to print with debug later
  yum:
    list: ansible
  register: result
- name: Install package with multiple repos enabled
  yum:
    name: sos
    enablerepo: "epel,ol7_latest"
- name: Install package with multiple repos disabled
  yum:
    name: sos
    disablerepo: "epel,ol7_latest"
- name: Download the nginx package but do not install it
  yum:
    name:
      - nginx
    state: latest
    download_only: true
'''
from ansible.module_utils.basic import AnsibleModule