Error when setting rand_init to False in some environments

[zchuning]

In the V2 push-wall, pick-place-wall, push-back, and shelf-place environments, setting rand_init to False and then resetting the environment would lead to the following error when calling step():

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/mnt/beegfs/home/zchuning/metaworld/metaworld/envs/mujoco/mujoco_env.py", line 25, in inner
    return func(*args, **kwargs)
  File "/mnt/beegfs/home/zchuning/metaworld/metaworld/envs/mujoco/sawyer_xyz/v2/sawyer_push_wall_v2.py", line 79, in evaluate_state
    ) = self.compute_reward(action, obs)
  File "/mnt/beegfs/home/zchuning/metaworld/metaworld/envs/mujoco/sawyer_xyz/v2/sawyer_push_wall_v2.py", line 157, in compute_reward
    object_grasped = self._gripper_caging_reward(
  File "/mnt/beegfs/home/zchuning/metaworld/metaworld/envs/mujoco/sawyer_xyz/sawyer_xyz_env.py", line 572, in _gripper_caging_reward
    caging_xz_margin = np.linalg.norm(self.obj_init_pos[xz] - self.init_tcp[xz])
TypeError: list indices must be integers or slices, not list

This is because the reset() function of these environments sets self.obj_init_pos to self.adjust_initObjPos(self.init_config['obj_init_pos']) when self.random_init is False (e.g. line 112 in sawyer_push_wall_v2.py). However, self.adjust_initObjPos() returns a python list instead of a numpy array. So line 572 of swyer_xyz_env.py triggers an error by accessing a python list with a list of indices.

A simple fix is to wrap a np.array() around self.adjust_initObjPos(self.init_config['obj_init_pos']), similar to how some other environments (e.g. Push V2) handle calls to fix_extreme_obs_pos(). But there might be a more systematic way to fix this, hence the github issue instead of a pull request.