Use timestamp based packagename always with -t
Use timestamp based packagename always with -t

Previously, package type (unstable, testing, stable)
were decided based on the git tag's status and -t
was only available in unstable commit.
With this change, we always use timestamp based
formatting when -t is given.

Change-Id: Id3f5097e424b9fe54d2efd17dc068e799e7cd6e6

midonet/python-midonetclient,midonet/python-midonetclient