Switch log.py's own logger to independant logger

[zagpat]

In case there is any kind of issue when setting up logger, use a specific logger for log calls. This avoids recursion issues when trying to operate "low level" calls on the logger we are actually working with. This specific logger logs to a temp file unrelated to the rest of sgtk log files to avoid file access issues and specific maintenance.

About the possible recusion issues (this works in debug mode):

• you initialize the base file handler
• there is an error while doing the rollover for the log file
• there's a call to log.debug
• log happens to be an instance of LogManager
• it needs to initialize the base file handler

You may get stuck in a recursive loop.

In the same spirit of avoiding issues while working on "low level" operations, specifying exceptions we're catching to avoid catching exceptions unrelated to current process (and especially KeyboardInterrupt and the likes)

[codecov]

Codecov Report

Merging #861 (e7b5bec) into master (5e0464f) will decrease coverage by 6.52%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master     #861      +/-   ##
==========================================
- Coverage   79.40%   72.88%   -6.53%     
==========================================
  Files         177      177              
  Lines       19322    19333      +11     
==========================================
- Hits        15343    14090    -1253     
- Misses       3979     5243    +1264     

Impacted Files	Coverage Δ
python/tank/log.py	88.82% <80.00%> (-1.06%)	⬇️
python/tank/commands/app_info.py	17.24% <0.00%> (-79.32%)	⬇️
python/tank/bootstrap/import_handler.py	18.18% <0.00%> (-73.74%)	⬇️
python/tank/commands/folders.py	20.00% <0.00%> (-69.10%)	⬇️
python/tank/commands/setup_project.py	17.32% <0.00%> (-66.29%)	⬇️
python/tank/commands/cache_yaml.py	31.57% <0.00%> (-52.64%)	⬇️
python/tank/commands/util.py	37.50% <0.00%> (-37.50%)	⬇️
python/tank/commands/core_localize.py	39.40% <0.00%> (-36.44%)	⬇️
python/tank/commands/unregister_folders.py	12.58% <0.00%> (-36.43%)	⬇️
python/tank/commands/tank_command.py	47.34% <0.00%> (-32.98%)	⬇️
... and 44 more

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