add zookeeper storage prefixing to support multi-cluster

[bdoyle0182]

Description

Similar to the recent kafka topic prefixing addition, we would like to be able to use the same zookeeper cluster for multiple openwhisk clusters without having the potential for invoker id clashes.

My changes affect the following components

• [ ] API
• [ ] Controller
• [ ] Message Bus (e.g., Kafka)
• [ ] Loadbalancer
• [X] Scheduler
• [X] Invoker
• [ ] Intrinsic actions (e.g., sequences, conductors)
• [ ] Data stores (e.g., CouchDB)
• [ ] Tests
• [ ] Deployment
• [ ] CLI
• [ ] General tooling
• [ ] Documentation

Types of changes

• [ ] Bug fix (generally a non-breaking change which closes an issue).
• [X] Enhancement or new feature (adds new functionality).
• [ ] Breaking change (a bug fix or enhancement which changes existing behavior).

Checklist:

• [X] I signed an Apache CLA.
• [X] I reviewed the style guides and followed the recommendations (Travis CI will check :).
• [ ] I added tests to cover my changes.
• [ ] My changes require further changes to the documentation.
• [ ] I updated the documentation where necessary.

[codecov-commenter]

Codecov Report

Merging #5226 (e11ea4d) into master (3e3414c) will decrease coverage by 3.59%. The diff coverage is 25.00%.

@@            Coverage Diff             @@
##           master    #5226      +/-   ##
==========================================
- Coverage   44.49%   40.89%   -3.60%     
==========================================
  Files         238      238              
  Lines       13957    13959       +2     
  Branches      570      556      -14     
==========================================
- Hits         6210     5709     -501     
- Misses       7747     8250     +503     

Impacted Files	Coverage Δ
...he/openwhisk/core/invoker/InstanceIdAssigner.scala	0.00% <0.00%> (ø)
.../scala/org/apache/openwhisk/core/WhiskConfig.scala	95.78% <100.00%> (+0.02%)	:arrow_up:
...pache/openwhisk/http/LenientSprayJsonSupport.scala	0.00% <0.00%> (-100.00%)	:arrow_down:
...g/apache/openwhisk/common/ResizableSemaphore.scala	0.00% <0.00%> (-88.47%)	:arrow_down:
...ache/openwhisk/utils/ExecutionContextFactory.scala	7.69% <0.00%> (-76.93%)	:arrow_down:
...n/scala/org/apache/openwhisk/utils/JsHelpers.scala	0.00% <0.00%> (-55.56%)	:arrow_down:
.../org/apache/openwhisk/common/NestedSemaphore.scala	27.27% <0.00%> (-54.55%)	:arrow_down:
...a/org/apache/openwhisk/core/entity/WhiskRule.scala	17.64% <0.00%> (-45.10%)	:arrow_down:
...org/apache/openwhisk/core/entity/WhiskEntity.scala	49.23% <0.00%> (-30.77%)	:arrow_down:
...rg/apache/openwhisk/core/entity/WhiskTrigger.scala	64.28% <0.00%> (-28.58%)	:arrow_down:
... and 46 more

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