Restore the MuJoCo env

[williamd4112]

In my case, I need to replicate the MuJoCo environment (for imitation learning). But, I find that the unpickled environment is not the same as the original environment. First, I pickled the environment which is used for expert's demonstration. Then I unpickled the environment for the learner and find that the initial observation of them are not the same.
I use the code below for testing.

env = gym.make('Reacher-v2')
with open('env.pkl', 'wb') as f:
    env = pickle.dump(env, f)
with open('env.pkl', 'rb') as f:
    load_env = pickle.load(f)
a = env.unwrapped._get_obs()
b = load_env.unwrapped._get_obs()
print(a-b)

Result:

[-5.93206753e-05 -2.84166611e-03 -1.08920995e-02  7.53343027e-02
 -2.19749669e-01  2.24585896e-02  2.24545317e-03  5.33221514e-04
  2.19514907e-01 -1.64562441e-02  0.00000000e+00]

[christopherhesse]

Looks like a duplicate of #402