ZTS: pool_checkpoint improvements

The pool_checkpoint tests may incorrectly fail because several of
them invoke zdb for an imported pool.  In this scenario it's not
unexpected for zdb to fail if the pool is modified.  To resolve
this these zdb checks are now done after the pool has been exported.

Additionally, the default cleanup functions assumed the pool would
be imported when they were run.  If this was not the case they're
exit early and fail to cleanup all of the test state causing
subsequent tests to fail.  Add a check to only destroy the pool
when it is imported.

Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#11832

tests/zfs-tests/tests/functional/pool_checkpoint/checkpoint_big_rewind.ksh

@@ -52,6 +52,7 @@ fragment_after_checkpoint_and_verify
 log_must zpool export $NESTEDPOOL
 log_must zpool import -d $FILEDISKDIR --rewind-to-checkpoint $NESTEDPOOL
 
-log_must zdb $NESTEDPOOL
+log_must zpool export $NESTEDPOOL
+log_must zdb -e -p $FILEDISKDIR $NESTEDPOOL
 
 log_pass "Rewind to checkpoint on a stressed pool."

tests/zfs-tests/tests/functional/pool_checkpoint/checkpoint_capacity.ksh

@@ -80,13 +80,14 @@ log_mustnot dd if=/dev/urandom of=$NESTEDFS0FILE bs=1M count=300
 #
 log_must zpool list $NESTEDPOOL
 
-log_must zdb -kc $NESTEDPOOL
-
 log_must zpool export $NESTEDPOOL
+log_must zdb -e -p $FILEDISKDIR -kc $NESTEDPOOL
+
 log_must zpool import -d $FILEDISKDIR --rewind-to-checkpoint $NESTEDPOOL
 
 log_must [ "$(head -c 100 $NESTEDFS0FILE)" = "$FILE0INTRO" ]
 
-log_must zdb $NESTEDPOOL
+log_must zpool export $NESTEDPOOL
+log_must zdb -e -p $FILEDISKDIR $NESTEDPOOL
 
 log_pass "Do not reuse checkpointed space at low capacity."

tests/zfs-tests/tests/functional/pool_checkpoint/checkpoint_discard_busy.ksh

@@ -104,7 +104,8 @@ set_tunable64 SPA_DISCARD_MEMORY_LIMIT 16777216
 
 nested_wait_discard_finish
 
-log_must zdb $NESTEDPOOL
+log_must zpool export $NESTEDPOOL
+log_must zdb -e -p $FILEDISKDIR $NESTEDPOOL
 
 log_pass "Can export/import but not rewind/checkpoint/discard or " \
     "change pool's config while discarding."

tests/zfs-tests/tests/functional/pool_checkpoint/pool_checkpoint.kshlib

@@ -154,13 +154,18 @@ function setup_nested_pools
 
 function cleanup_nested_pool
 {
-	log_must zpool destroy $NESTEDPOOL
+	if poolexists $NESTEDPOOL; then
+		log_must zpool destroy $NESTEDPOOL
+	fi
+
 	log_must rm -f $FILEDISKS
 }
 
 function cleanup_test_pool
 {
-	log_must zpool destroy $TESTPOOL
+	if poolexists $TESTPOOL; then
+		log_must zpool destroy $TESTPOOL
+	fi
 
 	#
 	# We always clear the labels of all disks