utils: add functions to get and set logging levels for tpm2-tss

[whooo]

Related to #49

I skipped support for TSS2_LOGFILE for now and due to how the logging works in libtss2 the loglevel can't be changed for a module as soon as that module have called a logging function

[codecov]

Codecov Report

Merging #161 (c9089d7) into master (07a92e9) will increase coverage by 0.15%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #161      +/-   ##
==========================================
+ Coverage   87.81%   87.96%   +0.15%     
==========================================
  Files          13       13              
  Lines        3382     3416      +34     
  Branches      318      325       +7     
==========================================
+ Hits         2970     3005      +35     
  Misses        277      277              
+ Partials      135      134       -1     

Impacted Files	Coverage Δ
tpm2_pytss/utils.py	87.50% <100.00%> (+4.94%)	⬆️
tpm2_pytss/FAPI.py	74.79% <0.00%> (+0.20%)	⬆️

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[joholl]

Cool, this is much needed!

I'm not sure if I forgot the fapijson log module or if it was added since then. We should add that.

[whooo]

@joholl, just pushed an update with fapijson and removed the "test" module as it only seems to be used for the tests

[joholl]

Hm, I thought about this a bit. I feel like a pythonic module should not write to stderr, at all. Instead, it should hand log records to the python standard lib logging module. This has many advantages: the user can have one log file for everything (including application-level logging), use the python log handlers and log levels, have one log format etc.

Have a look at draft #164.

Edit: as discussed in #164, this is solved best via callbacks. As for this PR: LGTM!

[whooo]

if something like tpm2-software/tpm2-tss#2087 is implemented I don't think this is needed