Disable history_004_pos

Occasionally observed failure of history_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 #7026 
Closes #7028

tests/zfs-tests/tests/functional/history/history_004_pos.ksh

@@ -31,6 +31,11 @@
 
 . $STF_SUITE/include/libtest.shlib
 
+# See issue: https://github.com/zfsonlinux/zfs/issues/7026
+if is_linux; then
+	log_unsupported "Test case occasionally fails"
+fi
+
 #
 # DESCRIPTION:
 #	'zpool history' can cope with simultaneous commands.