Illumos #3112, #3113, #3114

3112 ztest does not honor ZFS_DEBUG
3113 ztest should use watchpoints to protect frozen arc bufs
3114 some leaked nvlists in zfsdev_ioctl

Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Matt Amdur <Matt.Amdur@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <chris.siden@delphix.com>
Approved by: Eric Schrock <eric.schrock@delphix.com>

References:
  https://www.illumos.org/issues/3112
  https://www.illumos.org/issues/3113
  https://www.illumos.org/issues/3114
  illumos/illumos-gate@cd1c8b85eb

The /proc/self/cmd watchpoint interface is specific to Solaris.
Therefore, the #3113 implementation was reworked to use the more
portable mprotect(2) system call.  When the pages are watched they
are marked read-only for protection.  Any write to the protected
address range immediately trigger a SIGSEGV.  The pages are marked
writable again when they are unwatched.

Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1489

cmd/ztest/ztest.c

@@ -6210,11 +6210,12 @@ main(int argc, char **argv)
 
 	(void) setvbuf(stdout, NULL, _IOLBF, 0);
 
+	dprintf_setup(&argc, argv);
+
 	ztest_fd_rand = open("/dev/urandom", O_RDONLY);
 	ASSERT3S(ztest_fd_rand, >=, 0);
 
 	if (!fd_data_str) {
-		dprintf_setup(&argc, argv);
 		process_options(argc, argv);
 
 		setup_data_fd();