restapi: Commit remove brick if migrate executed

Modified the DELETE action which checks if there was a data migration
executed on the set of bricks being deleted. If so it executes the
commit operation on the same set of bricks.
If there was no migration executed earlier, its effectively a force
remove brick.

Change-Id: I7830749bb84f61dd1a80281d3abe6dc113150fd1
Signed-off-by: Shubhendu Tripathi <shtripat@redhat.com>