Handling of missing and stray log files in Bluefors Agent

[BrianJKoopman]

While this somewhat relates to ongoing development in #174, the underlying issues should still be fixed, either in that PR or a subsequent one.

I'll start with this log segment:

2021-06-03T05:20:00+0000 /logs/21-06-03/maxigauge 21-06-03.sync-conflict-20210603-011948-I2BQPMU.log not yet open, opening...
2021-06-03T05:20:00+0000 /logs/21-06-03/Flowmeter 21-06-03.sync-conflict-20210603-011958-I2BQPMU.log not yet open, opening...
2021-06-03T05:20:00+0000 Not publishing stale data. Make sure your log file sync is done at a rate faster than once ever 2 minutes.
2021-06-03T05:20:00+0000 Not publishing stale data. Make sure your log file sync is done at a rate faster than once ever 2 minutes.
2021-06-03T05:20:00+0000 Not publishing stale data. Make sure your log file sync is done at a rate faster than once ever 2 minutes.
...
...many more of these...
...
2021-06-03T05:20:03+0000 Not publishing stale data. Make sure your log file sync is done at a rate faster than once ever 2 minutes.
2021-06-03T05:20:03+0000 Not publishing stale data. Make sure your log file sync is done at a rate faster than once ever 2 minutes.
2021-06-03T09:00:59+0000 acq:0 Crash in thread: [Failure instance: Traceback: <class 'FileNotFoundError'>: [Errno 2] No such file or directory: '/logs/21-06-03/Flowmeter 21-06-03.log'
/usr/lib/python3.8/threading.py:932:_bootstrap_inner
/usr/lib/python3.8/threading.py:870:run
/usr/local/lib/python3.8/dist-packages/twisted/_threads/_threadworker.py:47:work
/usr/local/lib/python3.8/dist-packages/twisted/_threads/_team.py:181:doWork
--- <exception caught here> ---
/usr/local/lib/python3.8/dist-packages/twisted/python/threadpool.py:238:inContext
/usr/local/lib/python3.8/dist-packages/twisted/python/threadpool.py:254:<lambda>
/usr/local/lib/python3.8/dist-packages/twisted/python/context.py:118:callWithContext
/usr/local/lib/python3.8/dist-packages/twisted/python/context.py:83:callWithContext
bluefors_log_tracker.py:488:start_acq
bluefors_log_tracker.py:367:read_and_publish_logs
]
2021-06-03T09:00:59+0000 acq:0 Status is now "done".

There are two problems here:

1. The Agent matches files that we don't want to open (the sync-conflict files, a product of a syncing software in use in the Cornell setup)
2. The network file share, we believe, disappears briefly at some point, and the file we want to open goes missing. The monitoring process crashes when this happens.

The solutions would be to restrict the matching of filenames a bit more, and to catch and handle this exception properly, probably by logging a warning or error and trying again on the next loop.