Set DATA_DIR when running grenade.

And SWIFT_DATA_DIR because in stable/folsom devstack DATA_DIR
is not honored for SWIFT_DATA_DIR.  See bug 1162303.

Also combine duplicate conditionals.

Change-Id: Id3e7e6d7b44fb715db3bb15600473f776bc87440
Enable cinder on stable/folsom in grenade.

Grenade does not handle n-vol -> cinder upgrade, so only test
cinder -> cinder.

Change-Id: Ie00faf376449e5ae0a5de9ea56f85ac8c07b7a92