Doc: don't generate empty properties fields

Don't create empty properties fields in the resources samples.

This patch will help resolve niceness gates failures when generating the
docbook HOT reference.

Change-Id: I3c74fa583ac55dc0a23520ec07f5d07e3d1b6fab
Closes-Bug: #1360558
Added PublicDnsName verification in unit tests

Changed duplicate validation of attribute PrivateDnsName to verify
PublicDnsName instead in unit tests.

Change-Id: If9282f61a421ee6b79234c75d60b6b2b3dbc1ee1
correctly implement volumes_from property

The Docker plugin incorrectly implements the 'volumes_from' option:

- The property is marked as a string when it should be a list, and
- The property needs to be passed to start_container rather than
  create_container.

Change-Id: I617a4d29a9edbb45d80c7b8abb8f87eeaf795a8b
closes-bug: #1364041
closes-bug: #1364039
Merge "correctly implement volumes_from property"
Merge "Added PublicDnsName verification in unit tests"
Merge "Doc: don't generate empty properties fields"