Upgrades python version for cqlsh

[davidporter-id-au]

What changed?

• Added python3 dep via APK
• changed CQLSH installation to use pip3

Why?
cqlsh is broken

How did you test it?

➜  cadence docker images
REPOSITORY                   TAG                 IMAGE ID       CREATED              SIZE
ubercadence/cadence-canary   master              981cc1952c2c   About a minute ago   123MB
ubercadence/cadence-bench    master              1cc084161128   About a minute ago   117MB
ubercadence/cli              master              65b60f971e33   About a minute ago   94.8MB
ubercadence/server           master-auto-setup   7063ae11fc67   About a minute ago   371MB
ubercadence/server           master              25648ebb01d0   About a minute ago   277MB
➜  cadence docker run -ti  7063ae11fc67  cqlsh
Connection error: ('Unable to connect to any servers', {'127.0.0.1:9042': ConnectionRefusedError(111, "Tried connecting to [('127.0.0.1', 9042)]. Last error: Connection refused")})

Potential risks

Release notes

Documentation Changes

[davidporter-id-au]

after testing this wouldn't have actually caught the cqlsh issue, which fails at runtime only when executing, but it would have caught other issues, such as failure to correctly install to path.

[Groxx]

maybe pip3 install cqlsh && cqlsh --version so we don't make another layer?
but probably not a bad idea, since the install is far from a guarantee with python.

I suppose it's somewhat odd that there's no support for testing builds in dockerfiles 🤔

[davidporter-id-au]

I think normally you treat them as build artifacts and subject them to e2e testing as you would any other deployable

[Groxx]

yeah, though in-dockerfile would let you test things as you build rather than only at the end. e.g. for from scratch things, you could test in a build-and-debug-friendly env before you copy the binaries to a minimal image.

[Groxx]

great, thanks! simple fixes are always nice :)
and it's good to leave py2. it's definitely time to do so.

[coveralls]

Pull Request Test Coverage Report for Build 2e7767c2-235d-4c24-a4ff-f23a937c339e

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 74 unchanged lines in 14 files lost coverage.
• Overall coverage decreased (-0.02%) to 56.93%

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Files with Coverage Reduction	New Missed Lines	%
client/history/client.go	2	39.33%
client/history/metricClient.go	2	46.37%
common/task/weightedRoundRobinTaskScheduler.go	2	88.6%
common/types/mapper/thrift/shared.go	2	63.25%
service/history/handler.go	2	48.56%
service/matching/matcher.go	2	91.46%
common/cache/lru.go	3	90.73%
common/persistence/nosql/nosqlplugin/cassandra/workflow.go	3	55.49%
service/history/task/fetcher.go	3	86.67%
service/frontend/workflowHandler.go	4	59.4%

Totals
Change from base Build 44b36639-36d5-40b3-9df5-aa902204e7ff:	-0.02%
Covered Lines:	82904
Relevant Lines:	145625

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💛 - Coveralls