Update the gardener_addr flag (2 of 2)

[stephen-soltesz]

This change changes the -gardener_host flag to -gardener_addr to allow the caller to specify a host:port combination, typical of Go addresses. This change is a complement to https://github.com/m-lab/etl-gardener/pull/371 which allows gardener to specify the serving port. These changes should allow more flexibility in running the gardener and parser in local development modes and normalizing how addresses are specified in the etl pipeline.

This change additionally updates the k8s configuration that depends on the GARDENER_ADDR to specify both the address and port for the Gardener service.

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 7162

• 4 of 5 (80.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.03%) to 64.249%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cmd/etl_worker/etl_worker.go	4	5	80.0%
<!--	Total:	4	5	80.0%	-->

Files with Coverage Reduction	New Missed Lines	%
cmd/etl_worker/etl_worker.go	1	60.07%
<!--	Total:	1		-->

Totals
Change from base Build 7154:	0.03%
Covered Lines:	3853
Relevant Lines:	5997

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💛 - Coveralls