Split disk creation out of configure_swift()

Grenade needs to be able to configure Swift without initializing the
backing disk files.  Move it into create_swift_disk() and call
from init_swift().

Also move start of n-obj (if swift3 is not enabled) to start_nova().

Change-Id: Id33939182d84eeff10ba4139eeced2c1bc532f0f
Merge "Split disk creation out of configure_swift()"