we should use dh_python2, otherwise, the installation can go into
/usr/pyshared,
where as we are expecting to find the installation in
/usr/lib/python2.7

when using a build server with python-support installed, and if we
don't use dh_python2, contrail-openstack-dashboard installation fails

Change-Id: I1e7a98894815a1476b6a85d3ca139258df706da2
Closes-Bug: #1389038