Disable sparse_001_pos / truncate_001_pos.ksh on 32-bit systems

Commit 539d33c seems to have significantly increased the run time
of the sparse_001_pos.ksh and truncate_001_pos.ksh test cases on
32-bit systems.  This is likely due to dirty blocks from frees
being deferred to later txgs.

At the moment this is resulting in frequent failures on the
32-bit builders.  Disable this test case until the issue can be
analyzed and resolved.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #5727 
Closes #5728

tests/zfs-tests/tests/functional/sparse/sparse_001_pos.ksh

@@ -45,6 +45,11 @@
 
 verify_runnable "global"
 
+# See issue: https://github.com/zfsonlinux/zfs/issues/5727
+if is_32bit; then
+	log_unsupported "Test case slow on 32-bit systems"
+fi
+
 function cleanup
 {
 	[[ -e $TESTDIR ]] && log_must $RM -rf $TESTDIR/*

tests/zfs-tests/tests/functional/truncate/truncate_001_pos.ksh

@@ -42,6 +42,11 @@
 
 verify_runnable "global"
 
+# See issue: https://github.com/zfsonlinux/zfs/issues/5727
+if is_32bit; then
+	log_unsupported "Test case slow on 32-bit systems"
+fi
+
 function cleanup
 {
 	[[ -e $TESTDIR ]] && log_must $RM -rf $TESTDIR/*