Always restart devstack-gate when testing itself.

Devstack-gate was only restarting itself when the ZUUL_PROJECT was
devstack-gate. In the zuul gate queue projects are stacked and
ZUUL_PROJECT may be some other project when ZUUL_CHANGES includes a
change to devstack-gate. Restart devstack-gate whenever it is part of
ZUUL_CHANGES.

Change-Id: I1c34917bf2b1dbc732eb1d36c3b7c30a1d8822bd
Merge "Always restart devstack-gate when testing itself."