Merging local and remote bitmaps must be protected by hr_amp lock.

This is believed to fix hastd crashes, which might occur during
synchronization, triggered by the failed assertion:

 Assertion failed: (amp->am_memtab[ext] > 0),
 function activemap_write_complete, file activemap.c, line 351.

MFC after:	1 week
Make hastctl list command output current queue sizes.

Reviewed by:	pjd
MFC after:	1 month