Use RetryRule to mitigate test flakiness

[blindpirate]

Describe what this PR does / why we need it

In my previous #574 , I triggered travis build 3 times to get a successful result. This is too painful. This PR introduces RetryRule to retry tests in order to mitigate the test flakiness.

This is not a perfect solution (which should be rewriting the tests), but it's better than none.

A more modern alternative would be switching to JUnit 5 and using https://github.com/artsok/rerunner-jupiter .

Does this pull request fix one issue?

NONE

Describe how you did it

Create a RetryRule, which reruns failed test cases.

Tests for RetryRule are also added.

Describe how to verify it

Run travis build many times. There should be no flakiness anymore.

Special notes for reviews

Note: During retry, Before methods will be invoked, but the test class instance won't be reset.

[codecov-io]

Codecov Report

Merging #582 into master will increase coverage by 1.25%.
The diff coverage is 73.58%.

@@             Coverage Diff              @@
##             master     #582      +/-   ##
============================================
+ Coverage     39.86%   41.12%   +1.25%     
+ Complexity     1244     1215      -29     
============================================
  Files           275      267       -8     
  Lines          8702     7852     -850     
  Branches       1163     1062     -101     
============================================
- Hits           3469     3229     -240     
+ Misses         4785     4230     -555     
+ Partials        448      393      -55

Impacted Files	Coverage Δ	Complexity Δ
...re/src/main/java/com/alibaba/csp/sentinel/Env.java	75% <ø> (-5%)	1 <0> (ø)
...ain/java/com/alibaba/csp/sentinel/log/LogBase.java	69.64% <0%> (ø)	10 <0> (ø)	⬇️
...va/com/alibaba/csp/sentinel/init/InitExecutor.java	13.15% <0%> (+0.33%)	2 <0> (ø)	⬇️
.../sentinel/slots/nodeselector/NodeSelectorSlot.java	94.73% <100%> (ø)	4 <0> (ø)	⬇️
...nel/annotation/aspectj/SentinelResourceAspect.java	84.21% <100%> (ø)	3 <0> (?)
...sentinel/adapter/reactor/FluxSentinelOperator.java	100% <100%> (ø)	2 <0> (ø)	⬇️
...l/adapter/dubbo/fallback/DefaultDubboFallback.java	100% <100%> (ø)	2 <2> (?)
...tinel/slots/clusterbuilder/ClusterBuilderSlot.java	71.42% <100%> (ø)	8 <0> (ø)	⬇️
...l/annotation/aspectj/ResourceMetadataRegistry.java	83.33% <100%> (ø)	10 <2> (?)
.../sentinel/adapter/dubbo/DubboAppContextFilter.java	100% <100%> (ø)	3 <3> (?)
... and 42 more

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[blindpirate]

I added @Retry to all test cases of this class since I observed flaky failures in travis build history. I assume this is a common issue of all test cases in this class.

[blindpirate]

Hmmmm... seems not work well: https://travis-ci.org/alibaba/Sentinel/jobs/507205057

[sczyh30]

That's cool for auto-retrying unstable tests. Thanks! We might need to rewrite some of these tests later to be stable and time-independent (though it's tricky).