Add an element installing tuskar API service

This should make it easier to deploy tuskar in the undercloud
(basically, one will just add 'tuskar' the the list of elements
when building a disk image for the undercloud node).

This depends on Ib66e688bd7500f03dea7d4282607cd51078e9a51 to be
merged into tripleo-heat-templates to work properly.

Change-Id: I1d16e535ae50a06a8792e1613bb6b6c4647bf128
Merge "Add an element installing tuskar API service"