Add api docs to the rest client
Add api docs to the rest client

This commit adds docstrings for api documentation to the rest client.
Since this is a public interface we should document it.

Change-Id: I303d11bb1a9252f0815f295698b65fd01f90d969

sorenh/tempest-lib,cneill/tempest-lib,JioCloud/tempest-lib,varunarya10/tempest-lib