<!--- 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 -->

#
from __future__ import absolute_import, division, print_function
__metaclass__ = type
DOCUMENTATION = '''
---
module: dnf
version_added: 1.9
short_description: Manages packages with the I(dnf) package manager
description:
     - Installs, upgrade, removes, and lists packages and groups with the I(dnf) package manager.
options:
  name:
    description:
      - "A package name or package specifier with version, like C(name-1.0).
        When using state=latest, this can be '*' which means run: dnf -y update.
        You can also pass a url or a local path to a rpm file.
        To operate on several packages this can accept a comma separated string of packages or a list of packages."
      - Comparison operators for package version are valid here C(>), C(<), C(>=), C(<=). Example - C(name>=1.0)
    required: true
    aliases:
        - pkg
    type: list
    elements: str
  list:
    description:
      - Various (non-idempotent) commands for usage with C(/usr/bin/ansible) and I(not) playbooks. See examples.