ZTS: Fix snapshot_009_pos, snapshot_010_pos

Mitigate the likelihood of the newly created volumes being busy
when the 'zfs destroy -r' is issued by waiting for udev to settle.
Since this is not a iron clad fix I've added the test case to
the known list of possible failures and referenced issue #7961.

Finally, in the case this test does fail fix the cleanup logic
so subsequent tests won't incorrectly fail.

Reviewed-by: Giuseppe Di Natale <guss80@gmail.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #7961 
Closes #7962

tests/test-runner/bin/zts-report.py

@@ -264,6 +264,8 @@ maybe = {
     'rsend/rsend_024_pos': ['FAIL', '5665'],
     'rsend/send-c_volume': ['FAIL', '6087'],
     'snapshot/clone_001_pos': ['FAIL', known_reason],
+    'snapshot/snapshot_009_pos': ['FAIL', '7961'],
+    'snapshot/snapshot_010_pos': ['FAIL', '7961'],
     'snapused/snapused_004_pos': ['FAIL', '5513'],
     'tmpfile/setup': ['SKIP', tmpfile_reason],
     'threadsappend/threadsappend_001_pos': ['FAIL', '6136'],

tests/zfs-tests/include/libtest.shlib

@@ -642,7 +642,7 @@ function destroy_snapshot
 	typeset snap=${1:-$TESTPOOL/$TESTFS@$TESTSNAP}
 
 	if ! snapexists $snap; then
-		log_fail "'$snap' does not existed."
+		log_fail "'$snap' does not exist."
 	fi
 
 	#

tests/zfs-tests/tests/functional/snapshot/snapshot_009_pos.ksh

@@ -52,18 +52,15 @@ function cleanup
 	typeset snap
 
 	for ds in $ctr/$TESTVOL1 $ctr/$TESTCLONE; do
-		datasetexists $ds && \
-			log_must zfs destroy -f $ds
+		destroy_dataset $ds "-rf"
 	done
 
 	for snap in $ctr/$TESTFS1@$TESTSNAP1 \
 		$snappool $snapvol $snapctr $snapctrvol \
 		$snapctrclone $snapctrfs
 	do
-		snapexists $snap && \
-			log_must zfs destroy -rf $snap
+		snapexists $snap && destroy_dataset $snap "-rf"
 	done
-
 }
 
 log_assert "Verify snapshot -r can correctly create a snapshot tree."
@@ -91,6 +88,7 @@ else
 fi
 
 log_must zfs snapshot -r $snappool
+log_must block_device_wait
 
 #verify the snapshot -r results
 for snap in $snappool $snapfs $snapvol $snapctr $snapctrvol \

tests/zfs-tests/tests/functional/snapshot/snapshot_010_pos.ksh

@@ -49,15 +49,13 @@ function cleanup
 {
 	typeset snap
 
-	datasetexists $ctrvol && \
-		log_must zfs destroy -f $ctrvol
+	destroy_dataset $ctrvol "-rf"
 
 	for snap in $ctrfs@$TESTSNAP1 \
 		$snappool $snapvol $snapctr $snapctrvol \
 		$snapctrclone $snapctrfs
 	do
-		snapexists $snap && \
-			log_must zfs destroy -rf $snap
+		snapexists $snap && destroy_dataset $snap "-rf"
 	done
 
 }
@@ -85,6 +83,7 @@ else
 fi
 
 log_must zfs snapshot -r $snappool
+log_must block_device_wait
 
 #select the $TESTCTR as destroy point, $TESTCTR is a child of $TESTPOOL
 log_must zfs destroy -r $snapctr