don't use screen for grenade

now that the process stop pieces of devstack work much better,
it's not clear that we need to actually use screen to stuff in
the service starts / stops.

We should try to do this without screen.

Change-Id: Icc5b9b5f8dcde22f2864d3ba6aa91d0afe936d7a

devstack-vm-gate.sh

@@ -82,6 +82,7 @@ function setup_localrc {
     fi
 
     cat <<EOF >>localrc
+USE_SCREEN=False
 DEST=$BASE/$LOCALRC_OLDNEW
 ACTIVE_TIMEOUT=90
 BOOT_TIMEOUT=90
@@ -235,10 +236,6 @@ EOF
         # keystone deployed with mod wsgi cannot be upgraded or migrated
         # until https://launchpad.net/bugs/1365105 is resolved.
         echo "KEYSTONE_USE_MOD_WSGI=False" >> localrc
-    else
-        # Grenade needs screen, so only turn this off if we aren't
-        # running grenade.
-        echo "USE_SCREEN=False" >>localrc
     fi
 
     if [[ "$DEVSTACK_GATE_TEMPEST_LARGE_OPS" -eq "1" ]]; then