dmsetup: Support remove --deferred.

dmsetup: Support remove --deferred.

This patch adds a new flag --deferred to dmsetup remove. If this flag is
specified and the device is open, it is scheduled to be deleted on
close.

struct dm_info is extended.

The existing dm_task_get_info() is converted into a wrapper around the
new version dm_task_get_info_with_deferred_remove() so existing binaries
can still use the old smaller structure.

Recompiled code will pick up the new larger structure.

From: Mikulas Patocka <mpatocka@redhat.com>