Add doc support for OS-Services ext v2

Added doc support to os-services extension v2.
The ext allows to manage nova services.
This API has some internal internal inconsistencies that
prevent it from generating xml samples (they should be
available in v3).

Change-Id: I4922daabfbd3454439a07be1c425a52e0fddd821
Fixes: bug 1078015
Merge "Add doc support for OS-Services ext v2"