Exit sputnik with error code if checks fail

[marquiswang]

This allows scripts/tools to take the return result into account.

Furthermore, Extensions of sputnik like the sputnik-maven-plugin can use a return value of the Engine to communicate the result of a run and do something like fail a build.

Implement this by adding a Score object (with the review label and the score value as fields) and return that in Engine.run().

If a failing score value (< 0) is returned, then call System.exit with the score as the error status.

[codecov-io]

Codecov Report

Merging #205 into master will decrease coverage by 0.79%. The diff coverage is 66.96%.

@@             Coverage Diff             @@
##             master     #205     +/-   ##
===========================================
- Coverage     72.52%   71.72%   -0.8%     
- Complexity      592      608     +16     
===========================================
  Files           142      147      +5     
  Lines          1889     1956     +67     
  Branches        121      129      +8     
===========================================
+ Hits           1370     1403     +33     
- Misses          462      490     +28     
- Partials         57       63      +6

Impacted Files	Coverage Δ	Complexity Δ
...in/java/pl/touk/sputnik/engine/VisitorBuilder.java	100% <ø> (ø)	9 <0> (-5)	:arrow_down:
...c/main/java/pl/touk/sputnik/review/ReviewFile.java	92.3% <ø> (ø)	7 <0> (ø)	:arrow_down:
src/main/java/pl/touk/sputnik/engine/Engine.java	0% <0%> (ø)	0 <0> (ø)	:arrow_down:
src/main/java/pl/touk/sputnik/Main.java	0% <0%> (ø)	0 <0> (ø)	:arrow_down:
...ain/java/pl/touk/sputnik/connector/Connectors.java	0% <0%> (ø)	0 <0> (ø)	:arrow_down:
src/main/java/pl/touk/sputnik/review/Review.java	65% <100%> (ø)	13 <1> (+1)	:arrow_up:
.../java/pl/touk/sputnik/connector/ConnectorType.java	66.66% <100%> (+2.38%)	3 <0> (ø)	:arrow_down:
...a/pl/touk/sputnik/configuration/GeneralOption.java	98.36% <100%> (ø)	3 <0> (ø)	:arrow_down:
...ouk/sputnik/engine/score/ScoreStrategyFactory.java	100% <100%> (ø)	7 <7> (?)
...uk/sputnik/connector/local/LocalFacadeBuilder.java	14.28% <14.28%> (ø)	1 <1> (?)
... and 16 more

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[SpOOnman]

I've made a change in master branch that fixed one but so I guess you must rebase again.