pep8 changes to constraint.py

We need the code to pass pep8 tests so that we can
enable pep8 in Jenkins

Change-Id: I31e4bd10fad65735fabceaedcb1a3bd10e120153
Signed-off-by: Luis Pabon <lpabon@redhat.com>
Reviewed-on: http://review.gluster.org/5114
Reviewed-by: Peter Portante <pportant@redhat.com>
Tested-by: Peter Portante <pportant@redhat.com>