Fixes to errors/warnings raised by pylint 0.24

Running pylint 0.24.0 revealed 2 errors and 1 warning. Here is how I
fixed them:

* jqueue.py: silenced E1101
* netutils.py: rewrote the list comprehension using extend()
* watcher/__init__.py: fixed a missing format string parameter

These changes are backwards-compatible with pylint 0.21.1.

Signed-off-by: Andrea Spadaccini <spadaccio@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>