mvn_build: replace inline shell scriptlet with native python code

[decathorpe]

Note that this code is not compatible with python2, since the compress function in the gzip module is only available with python 3.2 and later.

Otherwise, the code should be equivalent to the original shell script (compression level 9 is the default in the python3 gzip module).

Compared to #45, here the whole output is collected in a string before it's written to stdout in one go. This should hopefully fix RPM messing up the output string by printing stuff in between the BEGIN and END headers.

If you want me to add the test cases from #45 here as well, I can do that.

Fixes #12 Hopefully fixes #72

[codecov-io]

Codecov Report

Merging #73 into master will decrease coverage by 0.1%. The diff coverage is 50%.

@@           Coverage Diff            @@
##           master    #73      +/-   ##
========================================
- Coverage   90.11%    90%   -0.11%     
========================================
  Files          43     43              
  Lines        3146   3153       +7     
========================================
+ Hits         2835   2838       +3     
- Misses        311    315       +4

Impacted Files	Coverage Δ
java-utils/mvn_build.py	80.39% <50%> (-2.77%)	:arrow_down:

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[mizdebsk]

Compatibility with Python 2.7 is a requirement - javapackages needs to be runnable on RHEL 7. And yes, I would like to see a test case for the new code.

[decathorpe]

Compatibility with Python 2.7 is a requirement - javapackages needs to be runnable on RHEL 7.

Alright, I will try to provide two different code paths for python2 and python3.

And yes, I would like to see a test case for the new code.

I'll add the tests from PR #45

[decathorpe]

Since RPM in fedora 31+ got fixed, this is pretty low priority for me now.

[mizdebsk]

Thanks for update. As RHEL 7 has reached "End of Full Support" milestone on August 6, 2019, we are discussing the possibility of dropping support for RHEL 7 and Python 2 in javapackages-tools. Therefore I will likely be able to merge this PR in near future.