do not reimplement built-in exceptions

Remove exceptions shadowing built-in ones from molecule.exceptions
and update the code to work with this change

molecule/exception.py

@@ -28,11 +28,5 @@ class MoleculeException(Exception):
         else:
             return repr(self.value)
 
-class EnvironmentError(MoleculeException):
-        """Environment error, self explanatory"""
-
 class SpecFileError(MoleculeException):
         """Error inside spec file"""
-
-class NotImplementedError(MoleculeException):
-        """Error inside spec file"""

molecule/settings.py

@@ -20,7 +20,7 @@
 from __future__ import with_statement
 import os
 import threading
-from molecule.exception import SpecFileError, EnvironmentError
+from molecule.exception import SpecFileError
 import molecule.utils
 
 class Constants(dict):

molecule/utils.py

@@ -23,7 +23,6 @@ import sys
 import time
 import subprocess
 import shutil
-from molecule.exception import EnvironmentError
 
 def get_year():
     return time.strftime("%Y")