Disable vdev_zaps_004_pos

Occasionally observed failure of vdev_zaps_004_pos due to the test
case not being 100% reliable.  In order to prevent false positives
disable this test case until it can be made reliable.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue openzfs#6935
Closes openzfs#6936

tests/zfs-tests/tests/functional/vdev_zaps/vdev_zaps_004_pos.ksh

@@ -31,6 +31,11 @@
 . $STF_SUITE/include/libtest.shlib
 . $STF_SUITE/tests/functional/vdev_zaps/vdev_zaps.kshlib
 
+# See issue: https://github.com/zfsonlinux/zfs/issues/6935
+if is_linux; then
+	log_unsupported "Test case occasionally fails"
+fi
+
 log_assert "Per-vdev ZAPs are transferred properly on attach/detach"
 
 DISK=${DISKS%% *}