re-enable shared memory connection for pybullet Gym envs (with fallback to GUI or DIRECT)

suppress shared memory connection warnings
add fallback from ER_BULLET_HARDWARE_OPENGL to TinyRenderer if not available

examples/pybullet/gym/pybullet_envs/bullet/bullet_client.py

@@ -8,7 +8,7 @@ class BulletClient(object):
 
   def __init__(self, connection_mode=pybullet.DIRECT):
     """Create a simulation and connect to it."""
-    self._client = -1 #pybullet.connect(pybullet.SHARED_MEMORY)
+    self._client = pybullet.connect(pybullet.SHARED_MEMORY)
     if(self._client<0):
       self._client = pybullet.connect(connection_mode)
     self._shapes = {}