Update to use Clouddocs plugin 1.7.2 in api-site poms

Modified all three poms and updated the version to 1.7.2
api-quick-start and api-ref were tested locally OK.
openstack-api-programming is built by a Jenkins job.

Change-Id: I2411adf429b86c08766684fb3d88e88bd8bec682
Added os-coverage extension

bug: #1103023

Change-Id: If3ca5fa75bd06692f444703676acc00b2052b6ff
author: Diane Fleming
Merge "Update to use Clouddocs plugin 1.7.2 in api-site poms"
Merge "Added os-coverage extension"