implement k8s service discovery (#988)

* implement k8s service discovery

* simplify code

* use default namespace if not provided

* disable codecov bot comment

* ignore adhoc dir

* simplify building target in NewClient

* reformat code

* Fix filepath (#990)

* format code, and reorg imports (#991)

* add more unit test

Co-authored-by: anqiansong <anqiansong@gmail.com>

core/proc/signals_test.go

@@ -0,0 +1,16 @@
+package proc
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDone(t *testing.T) {
+	select {
+	case <-Done():
+		assert.Fail(t, "should run")
+	default:
+	}
+	assert.NotNil(t, Done())
+}