[build] Improve build configuration for tests

[simonbasle]

• better common configuration
• clearer sequencing of events
• additional tests are more clearly segregated
  and will still run when explicitly called
• testNG is only exluded from check when
  building on Travis
• loops is always excluded from check when
  building a SNAPSHOT
• Travis fast_finish: do not wait for JDK9
  job to finish before setting the build status

[codecov-io]

Codecov Report

Merging #1007 into master will increase coverage by 0.04%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1007      +/-   ##
============================================
+ Coverage     83.67%   83.72%   +0.04%     
- Complexity     3390     3392       +2     
============================================
  Files           328      328              
  Lines         26744    26744              
  Branches       4937     4937              
============================================
+ Hits          22379    22391      +12     
+ Misses         2882     2875       -7     
+ Partials       1483     1478       -5

Impacted Files	Coverage Δ	Complexity Δ
...ain/java/reactor/core/publisher/MonoPublishOn.java	88.33% <0%> (-3.34%)	2% <0%> (ø)
...c/main/java/reactor/core/publisher/RingBuffer.java	70.56% <0%> (-0.95%)	24% <0%> (ø)
...rc/main/java/reactor/core/publisher/Operators.java	72.15% <0%> (+0.18%)	84% <0%> (+1%)	⬆️
...ava/reactor/core/publisher/WorkQueueProcessor.java	70.08% <0%> (+0.42%)	19% <0%> (ø)	⬇️
...ain/java/reactor/core/publisher/FluxPublishOn.java	87.84% <0%> (+0.62%)	5% <0%> (ø)	⬇️
...eactor/core/publisher/ParallelMergeSequential.java	81.34% <0%> (+1.03%)	7% <0%> (ø)	⬇️
.../java/reactor/core/scheduler/ElasticScheduler.java	90.62% <0%> (+2.08%)	20% <0%> (ø)	⬇️
...va/reactor/core/publisher/ParallelMergeReduce.java	71.9% <0%> (+3.3%)	3% <0%> (ø)	⬇️
...c/main/java/reactor/core/scheduler/WorkerTask.java	83.01% <0%> (+3.77%)	20% <0%> (+1%)	⬆️
.../java/reactor/core/publisher/FluxLimitRequest.java	98% <0%> (+4%)	5% <0%> (ø)	⬇️

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