Look for usable on-cluster credentials using k8schain (#243)

* dep ensure and use k8schain

* checkpoint

* fix vendoring, stuff builds

* Use k8schain for pushes too

* Use NewNoClient

* update ggcr dep

* Move k8schain usage to image_util.go

vendor/github.com/json-iterator/go/iter_array.go

@@ -0,0 +1,58 @@
+package jsoniter
+
+// ReadArray read array element, tells if the array has more element to read.
+func (iter *Iterator) ReadArray() (ret bool) {
+	c := iter.nextToken()
+	switch c {
+	case 'n':
+		iter.skipThreeBytes('u', 'l', 'l')
+		return false // null
+	case '[':
+		c = iter.nextToken()
+		if c != ']' {
+			iter.unreadByte()
+			return true
+		}
+		return false
+	case ']':
+		return false
+	case ',':
+		return true
+	default:
+		iter.ReportError("ReadArray", "expect [ or , or ] or n, but found "+string([]byte{c}))
+		return
+	}
+}
+
+// ReadArrayCB read array with callback
+func (iter *Iterator) ReadArrayCB(callback func(*Iterator) bool) (ret bool) {
+	c := iter.nextToken()
+	if c == '[' {
+		c = iter.nextToken()
+		if c != ']' {
+			iter.unreadByte()
+			if !callback(iter) {
+				return false
+			}
+			c = iter.nextToken()
+			for c == ',' {
+				if !callback(iter) {
+					return false
+				}
+				c = iter.nextToken()
+			}
+			if c != ']' {
+				iter.ReportError("ReadArrayCB", "expect ] in the end, but found "+string([]byte{c}))
+				return false
+			}
+			return true
+		}
+		return true
+	}
+	if c == 'n' {
+		iter.skipThreeBytes('u', 'l', 'l')
+		return true // null
+	}
+	iter.ReportError("ReadArrayCB", "expect [ or n, but found "+string([]byte{c}))
+	return false
+}