Misc small fixes after pylint checking

Change-Id: I85c7d98b0b717163ddefea35a2a022ce7c9c1973
diff --git a/drivers/common.py b/drivers/common.py
index f0d2128..1405f88 100644
--- a/drivers/common.py
+++ b/drivers/common.py
@@ -21,6 +21,8 @@
 import time
 import logging
 
+from errors import InputError, PExpectError
+
 class SwitchErrors:
     """ Error logging and statistics class """