Don't proceed further if domain does not exist

[adilhafeez]

This code change allows program to terminate as soon as it sees that domain does not exists. With this change error message is more clear. For example see this error message with this code change,

➜  cadence-samples git:(fail_fast) ✗ ./bin/helloworld -m worker
2019-10-16T23:15:01.957-0700    INFO    common/sample_helper.go:65  Logger created.
2019-10-16T23:15:01.958-0700    DEBUG   common/factory.go:131   Creating RPC dispatcher outbound    {"ServiceName": "cadence-frontend", "HostPort": "127.0.0.1:7933"}
2019-10-16T23:15:01.970-0700    FATAL   common/sample_helper.go:83  Domain doesn't exist    {"Domain": "samples-domain1", "error": "EntityNotExistsError{Message: Domain samples-domain1 does not exist.}"}
github.com/uber-common/cadence-samples/cmd/samples/common.(*SampleHelper).SetupServiceConfig
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/common/sample_helper.go:83
main.main
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/recipes/helloworld/main.go:40
runtime.main
    /usr/local/Cellar/go/1.12.9/libexec/src/runtime/proc.go:200
➜  cadence-samples git:(fail_fast) ✗

And without this code change here is the same error,

➜  cadence-samples git:(master) ✗ ./bin/helloworld -m worker
2019-10-16T23:14:33.330-0700    INFO    common/sample_helper.go:65  Logger created.
2019-10-16T23:14:33.330-0700    DEBUG   common/factory.go:131   Creating RPC dispatcher outbound    {"ServiceName": "cadence-frontend", "HostPort": "127.0.0.1:7933"}
2019-10-16T23:14:33.339-0700    INFO    common/sample_helper.go:83  Domain doesn't exist    {"Domain": "samples-domain1", "error": "EntityNotExistsError{Message: Domain samples-domain1 does not exist.}"}
2019-10-16T23:14:33.380-0700    ERROR   internal/internal_worker.go:244 domain does not exist   {"Domain": "samples-domain1", "TaskList": "helloWorldGroup", "WorkerID": "9488@ahafeez-mbp143@helloWorldGroup", "WorkerType": "DecisionWorker", "domain": "samples-domain1", "error": "EntityNotExistsError{Message: Domain samples-domain1 does not exist.}"}
go.uber.org/cadence/internal.verifyDomainExist.func1
    /Users/ahafeez/src/go/pkg/mod/go.uber.org/cadence@v0.8.9-0.20190711214419-cef99c5ba19e/internal/internal_worker.go:244
go.uber.org/cadence/internal/common/backoff.Retry
    /Users/ahafeez/src/go/pkg/mod/go.uber.org/cadence@v0.8.9-0.20190711214419-cef99c5ba19e/internal/common/backoff/retry.go:98
go.uber.org/cadence/internal.verifyDomainExist
    /Users/ahafeez/src/go/pkg/mod/go.uber.org/cadence@v0.8.9-0.20190711214419-cef99c5ba19e/internal/internal_worker.go:262
go.uber.org/cadence/internal.(*workflowWorker).Start
    /Users/ahafeez/src/go/pkg/mod/go.uber.org/cadence@v0.8.9-0.20190711214419-cef99c5ba19e/internal/internal_worker.go:357
go.uber.org/cadence/internal.(*aggregatedWorker).Start
    /Users/ahafeez/src/go/pkg/mod/go.uber.org/cadence@v0.8.9-0.20190711214419-cef99c5ba19e/internal/internal_worker.go:1004
github.com/uber-common/cadence-samples/cmd/samples/common.(*SampleHelper).StartWorkers
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/common/sample_helper.go:135
main.startWorkers
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/recipes/helloworld/main.go:21
main.main
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/recipes/helloworld/main.go:44
runtime.main
    /usr/local/Cellar/go/1.12.9/libexec/src/runtime/proc.go:200
2019-10-16T23:14:33.380-0700    ERROR   common/sample_helper.go:137 Failed to start workers.    {"error": "EntityNotExistsError{Message: Domain samples-domain1 does not exist.}"}
github.com/uber-common/cadence-samples/cmd/samples/common.(*SampleHelper).StartWorkers
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/common/sample_helper.go:137
main.startWorkers
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/recipes/helloworld/main.go:21
main.main
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/recipes/helloworld/main.go:44
runtime.main
    /usr/local/Cellar/go/1.12.9/libexec/src/runtime/proc.go:200
panic: Failed to start workers

goroutine 1 [running]:
github.com/uber-common/cadence-samples/cmd/samples/common.(*SampleHelper).StartWorkers(0xc00030e480, 0xc00002a100, 0xf, 0x182fdf6, 0xf, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/common/sample_helper.go:138 +0x2fd
main.startWorkers(...)
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/recipes/helloworld/main.go:21
main.main()
    /Users/ahafeez/src/go/src/github.com/uber-common/cadence-samples/cmd/samples/recipes/helloworld/main.go:44 +0x24b

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:white_check_mark: adilhafeez
:x: Groxx
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[Groxx]

aah, sorry - I didn't notice the CLA was needed because you're a new contributor.

@adilhafeez: if you click the details on that license/cla check, we just need that filled in and then it should run tests / pass / allow merging.