Switch from alpine to jessie-slim for runner utility images

[dgrove-oss]

The Alpine based images have a nasty problem with DNS failures that
tends to surface when running them in Kubernetes. After a fair amount
of poking around, it seems like the only reliable fix is to not use
Alpine images on Kubernetes until upstream bug fixes in various layers
of the software stack, including the Linux kernel propagate to the
Alpine releases. For more context,
see:
gliderlabs/docker-alpine#255
kubernetes/kubernetes#56903
https://www.weave.works/blog/racy-conntrack-and-dns-lookup-timeouts

[codecov-io]

Codecov Report

Merging #4052 into master will decrease coverage by 5.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4052      +/-   ##
==========================================
- Coverage   86.04%   80.88%   -5.16%     
==========================================
  Files         147      147              
  Lines        7173     7173              
  Branches      449      449              
==========================================
- Hits         6172     5802     -370     
- Misses       1001     1371     +370

Impacted Files	Coverage Δ
...core/database/cosmosdb/RxObservableImplicits.scala	0% <0%> (-100%)	⬇️
...core/database/cosmosdb/CosmosDBArtifactStore.scala	0% <0%> (-95.52%)	⬇️
...sk/core/database/cosmosdb/CosmosDBViewMapper.scala	0% <0%> (-92.6%)	⬇️
...whisk/core/database/cosmosdb/CosmosDBSupport.scala	0% <0%> (-83.34%)	⬇️
...abase/cosmosdb/CosmosDBArtifactStoreProvider.scala	0% <0%> (-58.83%)	⬇️
...ain/scala/whisk/core/invoker/InvokerReactive.scala	64.48% <0%> (-17.76%)	⬇️
...la/whisk/core/database/cosmosdb/CosmosDBUtil.scala	92% <0%> (-4%)	⬇️
...rc/main/scala/whisk/common/ForcibleSemaphore.scala	88.46% <0%> (+3.84%)	⬆️

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[csantanapr]

LGTM