[pantsd] In long-running processes, logging from PantsDaemon and its services leaks to the client.

[blorente]

After #7596, we have the case where, when DaemonPantsRunner sets up logging to redirect stdio through nailgun, the logging is set up globally. Therefore, we have the case where ouput from the daemon (say, a filesystem event) will get logged in the client, like so:

$ ./pants --enable-pantsd repl examples/src/python/example/hello::

14:43:21 00:00 [main]
...
14:43:25 00:04       [repl]

Python 3.7.2 (v3.7.2:9a3ffc0492, Dec 24 2018, 02:44:43)
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> a = 2 + 3
>>> 13:44:00 [INFO] enqueuing 1 changes for subscription all_files
13:44:00 [WARN] invalidation: cleared 2 and dirtied 254 nodes for: {"BUILD.tools", ""}

We may be able to use thread-local logging to ameliorate this issue, since it's a good proxy to determine whether a log statement is in a pants run (and therefore should go through nailgun to the client) or should go to the daemon.

[blorente]

Fixed