Make the code run in python3 environment

[rgayon]

• fix some string conversion errors in the python script
• force installation of python3 packages
• Apply https://github.com/boto/boto/pull/3699 manually to make the boto lib work with Py3 version of http lib

[codecov-io]

Codecov Report

Merging #76 into master will increase coverage by 0.37%. The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master      #76      +/-   ##
==========================================
+ Coverage   82.88%   83.25%   +0.37%     
==========================================
  Files          21       21              
  Lines        1332     1344      +12     
==========================================
+ Hits         1104     1119      +15     
+ Misses        228      225       -3

Impacted Files	Coverage Δ
auto_forensicate/hostinfo.py	60.71% <0%> (+8.86%)	:arrow_up:
auto_forensicate/recipes/disk.py	74.39% <0%> (-0.46%)	:arrow_down:
auto_forensicate/recipes/sysinfo.py	100% <100%> (ø)	:arrow_up:
tests/sysinfo_tests.py	100% <100%> (ø)	:arrow_up:

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