Merging two mkfs commands.
Merging two mkfs commands.

nova.disk.api.mkfs will use nova.utils.mkfs,
unless an arbitrary mkfs command has been provided by the user.
Preserving the default filesystem to be used for each os_type.

Also, adding run_as_root parameter to utils.mkfs, to allow it
handle block devices.

Change-Id: I3ca21e0ee80caa7e1152ebae56d73ed3c14844c0

n0ano/gantt,n0ano/gantt