code coverage in maven plugin

[petertrr]

What's done:

• More unit tests
• More integration tests
• Configured jacoco to generate reports for integration tests

This pull request closes #631

[codecov]

Codecov Report

Merging #644 (1679f28) into master (f6786c2) will increase coverage by 0.15%.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##             master     #644      +/-   ##
============================================
+ Coverage     78.91%   79.07%   +0.15%     
+ Complexity     1789     1787       -2     
============================================
  Files            88       88              
  Lines          4696     4697       +1     
  Branches       1506     1506              
============================================
+ Hits           3706     3714       +8     
+ Misses          298      288      -10     
- Partials        692      695       +3     

Flag	Coverage Δ	Complexity Δ
unittests	79.07% <50.00%> (+0.15%)	0.00 <0.00> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ	Complexity Δ
.../kotlin/org/cqfn/diktat/plugin/maven/DiktatMojo.kt	10.00% <0.00%> (ø)	0.00 <0.00> (ø)
...lin/org/cqfn/diktat/plugin/maven/DiktatBaseMojo.kt	21.05% <66.66%> (+13.90%)	0.00 <0.00> (-2.00)	⬆️

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[orchestr7]

now looks good, thanks!