S allius/issue334 (#335)

* move forward_at_cmd_resp into InfosG3P class

- the variable is shared between the two connections
of an inverter. One is for the TSUN cloud and the
other for the device.

* use inverter class to share values between
the two protocol instances of a proxy
- move forward_at_cmd_resp into class InverterG3P
- store inverter ptr in Solarman_V5 instances
- add inverter ptr to all constructurs of protocols
- adapt doku and unit tests-
- add integration tests for AT+ commands which
  check the forwarding from and to the TSUN cloud

* adapt and improve the unit tests
- fix node_id declaration, which always has a / at
  the end. See config grammar for this rule
- set global var test to default after test run

app/tests/test_inverter_g3.py

@@ -155,6 +155,7 @@ async def test_remote_except(config_conn, patch_open_connection):
         await asyncio.sleep(0)
         assert inverter.remote.stream==None
     del inverter
+    test  = MockType.RD_TEST_0_BYTES
 
     cnt = 0
     for inv in InverterBase: