Fix DEVSTACK_GATE_GRENADE values for sideways jobs

devstack-gate expects the value of DEVSTACK_GATE_GRENADE to be set
to more than just 'sideways'.  This adds the expected suffix to the
current experimental sideways grenade jobs.

Change-Id: I1398a13138754f8209d11e6bed0d14a5858a050c
Merge "Fix DEVSTACK_GATE_GRENADE values for sideways jobs"