app_queue: Fix deadlock between update and show queues

app_queue: Fix deadlock between update and show queues

Operations that update queues when shared_lastcall is set lock the
queue in question, then have to lock the queues container to find the
other queues with the same member. On the other hand, __queues_show
(which is called by both the CLI and AMI) does the reverse. It locks
the queues container, then iterates over the queues locking each in
turn to display them.  This creates a deadlock.

* Moved queue print logic from __queues_show to a separate function
  that can be called for a single queue.

* Updated __queues_show so it doesn't need to lock or traverse
  the queues container to show a single queue.

* Updated __queues_show to snap a copy of the queues container and iterate
  over that instead of locking the queues container and iterating over
  it while locked.  This prevents us from having to hold both the
  container lock and the queue locks at the same time.  This also
  allows us to sort the queue entries.

ASTERISK-29155

Change-Id: I78d4dc36728c2d7bc187b97d82673fc77f2bcf41