Fix resource mapping for Docker

resource_mapping() always returns all existing resource names and
their classes. available_resource_mapping() takes the dependencies
into account and only returns the ones whose dependencies have been
met.

Co-Authored-By: Richard Lee <rblee88@gmail.com>
Partial-Bug: #1271226
Change-Id: I3d785d92f1d30a3caf4cb0f7721c66c9dda294c3
Change Docker resource mapping name

Removing the OS:: prefix since this is not an OpenStack-provided
resource.  Also remove hardcoded resource mapping name in test.

Co-Authored-By: Anderson Mesquita <andersonvom@gmail.com>
Partial-Bug: #1271226
Change-Id: I5691a08df3700f896ca1fe6efec4487d44617d6d
Add Docker resources to docs

This add a section for Docker resources in the Template Guide page.

Co-Authored-By: Richard Lee <rblee88@gmail.com>
Change-Id: I912fbc8624d93f16e05cb00f886eed6142dd0793
Partial-Bug: #1271226
Merge "Fix resource mapping for Docker"
Merge "Change Docker resource mapping name"
Merge "Add Docker resources to docs"