ZTS: Test case failures

* large_dnode_008_pos - Force a pool sync before invoking zdb to
  ensure the updated dnode blocks have been persisted to disk.

* refreserv_raidz - Wait for the /dev/zvol links to be both created
  and removed, this is important because the same device volume
  names are being used repeatedly.

* btree_test - Add missing .gitignore file for btree_test binary.

Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #9769

tests/zfs-tests/cmd/btree_test/.gitignore

@@ -0,0 +1 @@
+/btree_test

tests/zfs-tests/tests/functional/features/large_dnode/large_dnode_008_pos.ksh

@@ -39,7 +39,7 @@ verify_runnable "both"
 
 function cleanup
 {
-	datasetexists $TEST_FS && log_must zfs destroy $TEST_FS
+	datasetexists $TEST_FS && destroy_dataset $TEST_FS
 }
 
 function verify_dnode_packing
@@ -71,6 +71,7 @@ for ((i=0; i < 100; i++)); do
 done
 
 log_must wait
+sync_pool $TESTPOOL
 
 verify_dnode_packing
 

tests/zfs-tests/tests/functional/refreserv/refreserv_raidz.ksh

@@ -121,6 +121,7 @@ for parity in 1 2 3; do
 			log_must test "$deltapct" -le $maxpct
 
 			log_must_busy zfs destroy "$vol"
+			block_device_wait
 		done
 
 		log_must_busy zpool destroy "$TESTPOOL"