python3 conversion: Use python 2 and 3 compatible exceptions

Without that we have:
  $ python3 pySim-read.py
  Using serial reader (port=/dev/ttyUSB0, baudrate=9600) interface
  Traceback (most recent call last):
    File "pySim-read.py", line 91, in <module>
      from pySim.transport.serial import SerialSimLink
    File "/home/gnutoo/work/projects/osmocom/pysim/pySim/transport/serial.py", line 29, in <module>
      from pySim.exceptions import NoCardError, ProtocolError
    File "/home/gnutoo/work/projects/osmocom/pysim/pySim/exceptions.py", line 26, in <module>
      import exceptions
  ModuleNotFoundError: No module named 'exceptions'

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>
Change-Id: Ie45dc7ccd72fe077ba3b424f221ff4ed02db436c

pySim/exceptions.py

@@ -23,14 +23,17 @@
 
 from __future__ import absolute_import
 
-import exceptions
+try:
-
+	# This is for compatibility with python 2 and 3
-
+	from exceptions import Exception
-class NoCardError(exceptions.Exception):
+except:
 	pass
 
-class ProtocolError(exceptions.Exception):
+class NoCardError(Exception):
 	pass
 
-class ReaderError(exceptions.Exception):
+class ProtocolError(Exception):
+	pass
+
+class ReaderError(Exception):
 	pass