Don't look for event counts with -V/validate

When running falco with -V/valdiate <rules file>, you won't get any
event counts. All prior tests didn't get this far as they also resulted
in rules parsing errors.

However, validating can now result in warnings only. This won't exit but
won't print event counts either.

Signed-off-by: Mark Stemm <mark.stemm@gmail.com>

test/falco_test.py

@@ -585,7 +585,8 @@ def test(self):
         self.check_rules_warnings(res)
         if len(self.rules_events) > 0:
             self.check_rules_events(res)
-        self.check_detections(res)
+        if len(self.validate_rules_file) == 0:
+            self.check_detections(res)
         if len(self.detect_counts) > 0:
             self.check_detections_by_rule(res)
         self.check_json_output(res)