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/[email protected]/internal/internal_worker.go:244
go.uber.org/cadence/internal/common/backoff.Retry
	/Users/ahafeez/src/go/pkg/mod/go.uber.org/[email protected]/internal/common/backoff/retry.go:98
go.uber.org/cadence/internal.verifyDomainExist
	/Users/ahafeez/src/go/pkg/mod/go.uber.org/[email protected]/internal/internal_worker.go:262
go.uber.org/cadence/internal.(*workflowWorker).Start
	/Users/ahafeez/src/go/pkg/mod/go.uber.org/[email protected]/internal/internal_worker.go:357
go.uber.org/cadence/internal.(*aggregatedWorker).Start
	/Users/ahafeez/src/go/pkg/mod/go.uber.org/[email protected]/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.