Sort modules in the package, add newline at EOF and defaults

The changes in this commit include:
- The modules in the __ini__.py file were sorted alphabetically.
- The new line at the end of file was added in randomized_env.py.
- Default values were assigned for VariationSpec, specifically for
fields method, distribution, mean_std and var_range. Fields xpath,
attrib, elem and default are specific to the model in the XML file
provided by the user, so they cannot be default parameters. Further
more, elem and default are obtained by parsing the XML file, so the user
won't set them.

rllab/envs/mujoco/dynamics_randomization/__init__.py

@@ -1,5 +1,4 @@
-from rllab.envs.mujoco.dynamics_randomization.variation import Variations
-from rllab.envs.mujoco.dynamics_randomization.variation import Method
-from rllab.envs.mujoco.dynamics_randomization.variation import Distribution
-from rllab.envs.mujoco.dynamics_randomization.mujoco_model_generator import MujocoModelGenerator
 from rllab.envs.mujoco.dynamics_randomization.randomized_env import randomize
+from rllab.envs.mujoco.dynamics_randomization.variation import Distribution
+from rllab.envs.mujoco.dynamics_randomization.variation import Method
+from rllab.envs.mujoco.dynamics_randomization.variation import Variations

rllab/envs/mujoco/dynamics_randomization/randomized_env.py

@@ -84,4 +84,4 @@ def horizon(self):
         return self._wrapped_env.horizon
 
 
-randomize = RandomizedEnv
+randomize = RandomizedEnv

rllab/envs/mujoco/dynamics_randomization/variation.py

@@ -31,12 +31,12 @@ class works more like a data structure to store the data fields required
     """
 
     def __init__(self,
-                 xpath=None,
-                 attrib=None,
-                 method=None,
-                 distribution=None,
-                 var_range=None,
-                 mean_std=None,
+                 xpath,
+                 attrib,
+                 method,
+                 distribution,
+                 var_range,
+                 mean_std,
                  elem=None,
                  default=None):
 
@@ -209,10 +209,10 @@ def __init__(self, variations):
         self._variations = variations
         self._xpath = None
         self._attrib = None
-        self._method = None
-        self._distribution = None
-        self._mean_std = None
-        self._var_range = None
+        self._method = Method.ABSOLUTE
+        self._distribution = Distribution.UNIFORM
+        self._mean_std = (0.0, 1.0)
+        self._var_range = (0.0, 1.0)
         self._elem = None
         self._default = None