Skip tests that are slow on 32-bit builders

zpool_create_024_pos, zvol_misc_002_pos, write_dirs_002_pos are slow
on the buildbot 32-bit builder. Skip the test cases for now on 32-bit
builders.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Closes #6195

tests/zfs-tests/tests/functional/cli_root/zpool_create/zpool_create_024_pos.ksh

@@ -39,6 +39,10 @@
 
 verify_runnable "global"
 
+if is_32bit; then
+	log_unsupported "Test case runs slowly on 32 bit"
+fi
+
 function cleanup
 {
 	if [[ -n "$child_pids" ]]; then

tests/zfs-tests/tests/functional/write_dirs/write_dirs_002_pos.ksh

@@ -46,6 +46,10 @@
 
 verify_runnable "both"
 
+if is_32bit; then
+	log_unsupported "Test case runs slowly on 32 bit"
+fi
+
 function cleanup
 {
 	for file in `find $TESTDIR -type f`; do

tests/zfs-tests/tests/functional/zvol/zvol_misc/zvol_misc_002_pos.ksh

@@ -44,6 +44,10 @@
 
 verify_runnable "global"
 
+if is_32bit; then
+	log_unsupported "Test case runs slowly on 32 bit"
+fi
+
 volsize=$(zfs get -H -o value volsize $TESTPOOL/$TESTVOL)
 
 function cleanup
@@ -88,7 +92,7 @@ done
 
 if is_linux; then
 	EXIT_STATUS=4
-	sync
+	log_must sync
 else
 	EXIT_STATUS=39
 	log_must lockfs -f $TESTDIR