contrib/rpc_examples: add example for python3

Halt, resume, memory read/write are used in various ways.

Change-Id: Ia6727678bfc19cc764f822b739bddaae56e9dc70
Signed-off-by: Andreas Ortmann <ortmann@finf.uni-hannover.de>
Reviewed-on: http://openocd.zylin.com/2000


Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>