connect: interpolate task env in config values

When configuring Consul Service Mesh, it's sometimes necessary to
provide dynamic value that are only known to Nomad at runtime. By
interpolating configuration values (in addition to configuration keys),
user are able to pass these dynamic values to Consul from their Nomad
jobs.

client/taskenv/services.go

@@ -81,7 +81,12 @@ func interpolateMapStringInterface(taskEnv *TaskEnv, orig map[string]interface{}
 
 	m := make(map[string]interface{}, len(orig))
 	for k, v := range orig {
-		m[taskEnv.ReplaceEnv(k)] = v
+		envK := taskEnv.ReplaceEnv(k)
+		if vStr, ok := v.(string); ok {
+			m[envK] = taskEnv.ReplaceEnv(vStr)
+		} else {
+			m[envK] = v
+		}
 	}
 	return m
 }

client/taskenv/services_test.go

@@ -239,6 +239,7 @@ func TestInterpolate_interpolateConnect(t *testing.T) {
 				},
 				Config: map[string]interface{}{
 					"${config1}": 1,
+					"port":       "${port1}",
 				},
 			},
 		},
@@ -347,6 +348,7 @@ func TestInterpolate_interpolateConnect(t *testing.T) {
 				},
 				Config: map[string]interface{}{
 					"_config1": 1,
+					"port":     "12345",
 				},
 			},
 		},