Add ability to filter events by priority/cleanups

Clean up the handling of priority levels within rules. It used to be a
mix of strings handled in various places. Now, in falco_common.h there's
a consistent type for priority-as-number as well as a list of
priority-as-string values. Priorities are passed around as numbers
instead of strings. It's still permissive about capitalization.

Also add the ability to load rules by severity. New falco
config option "priority=<val>"/-o priority=<val> specifies the minimum
priority level of rules that will be loaded.

Add unit tests for same. The test suppresses INFO notifications for a
rule/trace file combination that would otherwise generate them.

test/falco_test.py

@@ -30,6 +30,7 @@ class FalcoTest(Test):
             self.trace_file = os.path.join(self.basedir, self.trace_file)
 
         self.json_output = self.params.get('json_output', '*', default=False)
+        self.priority = self.params.get('priority', '*', default='debug')
         self.rules_file = self.params.get('rules_file', '*', default=os.path.join(self.basedir, '../rules/falco_rules.yaml'))
 
         if not isinstance(self.rules_file, list):
@@ -347,8 +348,8 @@ class FalcoTest(Test):
             trace_arg = "-e {}".format(self.trace_file)
 
         # Run falco
-        cmd = '{} {} {} -c {} {} -o json_output={} -v'.format(
-            self.falco_binary_path, self.rules_args, self.disabled_args, self.conf_file, trace_arg, self.json_output)
+        cmd = '{} {} {} -c {} {} -o json_output={} -o priority={} -v'.format(
+            self.falco_binary_path, self.rules_args, self.disabled_args, self.conf_file, trace_arg, self.json_output, self.priority)
 
         for tag in self.disable_tags:
             cmd += ' -T {}'.format(tag)

test/falco_tests.yaml

@@ -129,6 +129,21 @@ trace_files: !mux
       - rules/double_rule.yaml
     trace_file: trace_files/cat_write.scap
 
+  multiple_rules_suppress_info:
+    detect: True
+    detect_level:
+      - WARNING
+      - ERROR
+    priority: WARNING
+    detect_counts:
+      - open_from_cat: 8
+      - exec_from_cat: 1
+      - access_from_cat: 0
+    rules_file:
+      - rules/single_rule.yaml
+      - rules/double_rule.yaml
+    trace_file: trace_files/cat_write.scap
+
   multiple_rules_overriding:
     detect: False
     rules_file: