add namespace param for fn and env (#2556)

This PR moves fission CLI as closer as possible to kubectl command behaviour.  We have improved namespace handling behaviour across CLI.

* add namespace param for fn and env
* use common fn for ns check
* update validation
* default namespace for httpTrigger, env and package, config and triggers
* use default ns
* add namespace filter to spec
* add forceNamespace flag
* set current namespace
* add default namespace in config
* add namespace specific destroy
* add all namespace in the list of resources
* add namespace as global tag
* use %s instead of %v
* add test cases for namespace
* use ns in get all functions

pkg/fission-cli/util/util_test.go

@@ -64,3 +64,11 @@ func TestGetEnvVarFromStringSlice(t *testing.T) {
 		})
 	}
 }
+
+func TestGetConfig(t *testing.T) {
+	response, err := GetKubernetesNamespace("")
+	if err != nil {
+		t.Log(err)
+	}
+	t.Log("Current NS: ", response)
+}