message: changing unsetenv in common.py
diff: @@ -109,7 +109,7 @@ class NgraphTest(object):
  # unset the env variable
  def unset_env_variable(self, env_var):
  - os.environ.pop(env_var, None)
  + os.unsetenv(env_var)
  print("Unset env variable ", env_var)
  # get the env variable
  