Parse system time into datetime object

Instead of returning the datetime as a string, parse it and return a
datetime object.

See: #46

nethsm/__init__.py

@@ -993,12 +993,12 @@ def get_config_network(self) -> NetworkConfig:
             netmask=response.body.netmask,
         )
 
-    def get_config_time(self) -> str:
+    def get_config_time(self) -> datetime:
         try:
             response = self.get_api().config_time_get()
         except Exception as e:
             _handle_exception(e, state=State.OPERATIONAL, roles=[Role.ADMINISTRATOR])
-        return response.body.time
+        return datetime.fromisoformat(response.body.time)
 
     def get_config_unattended_boot(self) -> str:
         try:

tests/test_nethsm_config.py

@@ -32,9 +32,7 @@ def get_config_network(nethsm: NetHSM) -> None:
 
 
 def get_config_time(nethsm: NetHSM) -> None:
-    dt_nethsm = datetime.datetime.strptime(
-        nethsm.get_config_time(), "%Y-%m-%dT%H:%M:%SZ"
-    ).replace(tzinfo=datetime.timezone.utc)
+    dt_nethsm = nethsm.get_config_time()
     dt_now = datetime.datetime.now(datetime.timezone.utc)
 
     seconds_diff = (dt_nethsm - dt_now).total_seconds()