core: hide registerHandler (#964)

* core: hide registerHandler

Remove RegisterHandler and just make it implicit when we look at the
handler compilation step.

* Rename GetHandler to just Handler

Update callers and make auto check Hander in OnStartup.

* Up test coverage in erratic

* up test coverage

middleware/erratic/setup_test.go

@@ -47,14 +47,33 @@ func TestParseErratic(t *testing.T) {
 			delay 3 1ms
 
 		}`, false, 0, 3, 2},
+		{`erraric {
+			drop 3
+			delay
+		}`, false, 3, 2, 0},
 		// fails
 		{`erratic {
 			drop -1
 		}`, true, 0, 0, 0},
+		{`erratic {
+			delay -1
+		}`, true, 0, 0, 0},
+		{`erratic {
+			delay 1 2 4
+		}`, true, 0, 0, 0},
+		{`erratic {
+			delay 15.a
+		}`, true, 0, 0, 0},
 		{`erraric {
 			drop 3
 			delay 3 bla
 		}`, true, 0, 0, 0},
+		{`erraric {
+			truncate 15.a
+		}`, true, 0, 0, 0},
+		{`erraric {
+			something-else
+		}`, true, 0, 0, 0},
 	}
 	for i, test := range tests {
 		c := caddy.NewTestController("dns", test.input)