class variable for API verison, fix env tests (#2817)

ml-agents-envs/mlagents/envs/environment.py

     SCALAR_ACTION_TYPES = (int, np.int32, np.int64, float, np.float32, np.float64)
     SINGLE_BRAIN_ACTION_TYPES = SCALAR_ACTION_TYPES + (list, np.ndarray)
     SINGLE_BRAIN_TEXT_TYPES = list
+    API_VERSION = "API-11"
 
     def __init__(
         self,
         atexit.register(self._close)
         self.port = base_port + worker_id
         self._buffer_size = 12000
-        self._version_ = "API-11"
+        self._version_ = UnityEnvironment.API_VERSION
         self._loaded = (
             False
         )  # If true, this means the environment was successfully loaded

ml-agents-envs/mlagents/envs/mock_communicator.py

 from .communicator import Communicator
+from .environment import UnityEnvironment
 from mlagents.envs.communicator_objects.unity_rl_output_pb2 import UnityRLOutputProto
 from mlagents.envs.communicator_objects.brain_parameters_pb2 import BrainParametersProto
 from mlagents.envs.communicator_objects.unity_rl_initialization_output_pb2 import (
             is_training=True,
         )
         rl_init = UnityRLInitializationOutputProto(
-            name="RealFakeAcademy", version="API-10", log_path="", brain_parameters=[bp]
+            name="RealFakeAcademy",
+            version=UnityEnvironment.API_VERSION,
+            log_path="",
+            brain_parameters=[bp],
         )
         output = UnityRLOutputProto(agentInfos=self._get_agent_infos())
         return UnityOutputProto(rl_initialization_output=rl_init, rl_output=output)