Adds tracing of async and background operations

[elgris]

1. Async messaging between ZMON scheduler and ZMON worker
2. Background updating of cached repositories

[codecov[bot]]

Codecov Report

Merging #82 into master will increase coverage by 0.93%. The diff coverage is 73.91%.

@@             Coverage Diff              @@
##             master      #82      +/-   ##
============================================
+ Coverage     19.41%   20.34%   +0.93%     
- Complexity      153      154       +1     
============================================
  Files            92       92              
  Lines          2277     2290      +13     
  Branches        230      232       +2     
============================================
+ Hits            442      466      +24     
+ Misses         1796     1785      -11     
  Partials         39       39

Impacted Files	Coverage Δ	Complexity Δ
...ando/zmon/scheduler/ng/checks/CheckRepository.java	0% <0%> (ø)	0 <0> (ø)	:arrow_down:
...ando/zmon/scheduler/ng/alerts/AlertRepository.java	9.25% <0%> (ø)	1 <0> (ø)	:arrow_down:
...ndo/zmon/scheduler/ng/config/SchedulerFactory.java	0% <0%> (ø)	0 <0> (ø)	:arrow_down:
...cheduler/ng/config/QueueSelectorConfiguration.java	0% <0%> (ø)	0 <0> (ø)	:arrow_down:
...zalando/zmon/scheduler/ng/queue/QueueSelector.java	0% <0%> (ø)	0 <0> (ø)	:arrow_down:
...zalando/zmon/scheduler/ng/scheduler/Scheduler.java	47.16% <100%> (ø)	11 <0> (ø)	:arrow_down:
...e/zalando/zmon/scheduler/ng/CommandSerializer.java	47.14% <100%> (ø)	3 <1> (ø)	:arrow_down:
...o/zmon/scheduler/ng/entities/EntityRepository.java	59.64% <50%> (ø)	23 <0> (ø)	:arrow_down:
...de/zalando/zmon/scheduler/ng/CachedRepository.java	37.03% <71.42%> (+2.25%)	3 <0> (ø)	:arrow_down:
...ava/de/zalando/zmon/scheduler/ng/CeleryWriter.java	80% <88.88%> (+45.51%)	4 <1> (+1)	:arrow_up:

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[vetinari]

:+1:

[elgris]

👍