Refactor mock-data for weather-tests generation (#3000)

Refactored the mock data generation for the tests so we can use plain
JSON files for the data and read it in a more general way.

Comments welcome!

Co-authored-by: veeck <michael@veeck.de>

tests/mocks/weather_current.json

@@ -0,0 +1,48 @@
+{
+	"coord": {
+		"lon": 11.58,
+		"lat": 48.14
+	},
+	"weather": [
+		{
+			"id": 615,
+			"main": "Snow",
+			"description": "light rain and snow",
+			"icon": "13d"
+		},
+		{
+			"id": 500,
+			"main": "Rain",
+			"description": "light rain",
+			"icon": "10d"
+		}
+	],
+	"base": "stations",
+	"main": {
+		"temp": 1.49,
+		"pressure": 1005,
+		"humidity": 93.7,
+		"temp_min": 1,
+		"temp_max": 2
+	},
+	"visibility": 7000,
+	"wind": {
+		"speed": 11.8,
+		"deg": 250
+	},
+	"clouds": {
+		"all": 75
+	},
+	"dt": 1547387400,
+	"sys": {
+		"type": 1,
+		"id": 1267,
+		"message": 0.0031,
+		"country": "DE",
+		"sunrise": 1547362817,
+		"sunset": 1547394301
+	},
+	"id": 2867714,
+	"name": "Munich",
+	"cod": 200
+}