[#318] Log unmatched requests

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

api/middleware/policy.go

@@ -293,7 +293,7 @@ func determineBucketOperation(r *http.Request) string {
 		}
 	}
 
-	return ""
+	return "UnmatchedBucketOperation"
 }
 
 func determineObjectOperation(r *http.Request) string {
@@ -357,12 +357,12 @@ func determineObjectOperation(r *http.Request) string {
 		}
 	}
 
-	return ""
+	return "UnmatchedObjectOperation"
 }
 
 func determineGeneralOperation(r *http.Request) string {
 	if r.Method == http.MethodGet {
 		return ListBucketsOperation
 	}
-	return ""
+	return "UnmatchedOperation"
 }