target: Introduce a function that shows the command state

Introduce target_show_cmd() and use it where appropriate. If
transport_wait_for_tasks() takes too long, make it show the
state of the command it is waiting for.

(Add missing brackets around multi-line conditions - nab)

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andy Grover <agrover@redhat.com>
Cc: David Disseldorp <ddiss@suse.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>