Add test for enabled flag.

New test case disables a rule that would otherwise match.

test/rules/single_rule_enabled_flag.yaml

@@ -0,0 +1,9 @@
+- macro: is_cat
+  condition: proc.name=cat
+
+- rule: open_from_cat
+  desc: A process named cat does an open
+  condition: evt.type=open and is_cat
+  output: "An open was seen (command=%proc.cmdline)"
+  priority: WARNING
+  enabled: false