poller-wrapper.py fails to log when log file is a fifo pipe in python 3

When the log file is a named fifo pipe or stdout (for injecting logs directly into journald) and the poller wrapper is running on Python 3, it fails with an "OSError: [Errno 29] Illegal seek" on the `f = open(log_path,'a')` line.

This is a known but unsolved python 3 bug as can be seen here https://bugs.python.org/issue27805 and https://bugs.python.org/issue20074.

The solution we used for now is to overwrite the open function to the open mode if appropriate, we did not want to modify the poller-wrapper directly to avoid issues with upgrades.

`python3 poller-wrapper-wrapper.py poller-wrapper.py -w 10`

poller-wrapper-wrapper.py is attached.