Adjust the keeping duration.

[style95]

Description

This is to reduce the keeping duration.
In FPCScheduler, this value is used to decide how much time do we keep the warmed container.
Currently, it is 60 minutes and it means after a timeout of paused container(10mins), it will keep the last container for another 60 minutes.
I think this is not a good value for the default.
In many cases that people develop or test OpenWhisk, there would be fewer resources in their dev environment and this would cause out of resources easily.

My changes affect the following components

• API
• Controller
• Message Bus (e.g., Kafka)
• Loadbalancer
• Scheduler
• 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).
• Enhancement or new feature (adds new functionality).
• Breaking change (a bug fix or enhancement which changes existing behavior).

Checklist:

• I signed an Apache CLA.
• 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 #5208 (8a1423c) into master (829e734) will increase coverage by 17.71%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #5208       +/-   ##
===========================================
+ Coverage   44.06%   61.78%   +17.71%     
===========================================
  Files         238      238               
  Lines       13957    13957               
  Branches      570      570               
===========================================
+ Hits         6150     8623     +2473     
+ Misses       7807     5334     -2473     

Impacted Files	Coverage Δ
...che/openwhisk/core/invoker/LogStoreCollector.scala	0.00% <0.00%> (-100.00%)	⬇️
...hisk/core/scheduler/message/ContainerMessage.scala	0.00% <0.00%> (-100.00%)	⬇️
.../openwhisk/core/scheduler/FPCSchedulerServer.scala	0.00% <0.00%> (-95.84%)	⬇️
...nwhisk/core/scheduler/queue/ContainerCounter.scala	0.00% <0.00%> (-92.11%)	⬇️
...sk/core/scheduler/container/ContainerManager.scala	0.00% <0.00%> (-88.72%)	⬇️
...a/org/apache/openwhisk/http/BasicHttpService.scala	3.17% <0.00%> (-87.31%)	⬇️
...e/openwhisk/core/scheduler/queue/MemoryQueue.scala	0.00% <0.00%> (-83.74%)	⬇️
.../core/scheduler/container/CreationJobManager.scala	0.00% <0.00%> (-83.34%)	⬇️
...scheduler/queue/ElasticSearchDurationChecker.scala	0.00% <0.00%> (-80.77%)	⬇️
.../main/scala/org/apache/openwhisk/core/WarmUp.scala	21.42% <0.00%> (-78.58%)	⬇️
... and 156 more

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[bdoyle0182]

LGTM