mkfs.gfs2: print message about BKLDISCARD ioctl taking a long time
When running mkfs.gfs2 the BLKDISCARD ioctl() can sit waiting for a
long time without feedback.
Added a message in mkfs.gfs2 to the user just before the ioctl begins
to warn the user that the operation could take a while to complete.
Signed-off-by: Paul Evans <pevans@redhat.com>