Fix fd leak from get_logger() in python 2.6

Calling get_logger({}) instantiates a logging.handlers.SyslogHandler,
which opens and keeps a socket around (either /dev/log or UDP or
whatever; not important).

Under Python 2.6, all logging handlers instantiated anywhere at all
will live for the entire lifetime of the program; they get stored in
logging._handlerList and logging._handlers. Python 2.7 is very
similar, but uses weakrefs instead of strong references in those
module-level variables, so logging handlers can actually get cleaned
up prior to program exit.

The net effect is that any program that calls get_logger() more than a
fixed number of times will leak file descriptors under Python 2.6.

This commit throws encapsulation out the window and, under 2.6 only,
replaces strong references with weakrefs in logging._handlerList and
logging._handlers, thus avoiding the leak.

Change-Id: I5dc0d1619c5a4500f892b898afd9e3668ec0ee7c
Merge "Fix fd leak from get_logger() in python 2.6"