Fix generation of http proxy configuration
Fix generation of http proxy configuration

The dcos-config.yaml template was failing to generated
valid yaml when we included some proxy configuraiton.

Fixes https://dcosjira.atlassian.net/browse/DCOS-387

surdy/dcos,mesosphere-mergebot/dcos,lingmann/dcos,kensipe/dcos,darkonie/dcos,mnaboka/dcos,asridharan/dcos,vishnu2kmohan/dcos,branden/dcos,amitaekbote/dcos,lingmann/dcos,mnaboka/dcos,lingmann/dcos,dcos/dcos,xinxian0458/dcos,vishnu2kmohan/dcos,darkonie/dcos,mesosphere-mergebot/dcos,surdy/dcos,mesosphere-mergebot/mergebot-test-dcos,surdy/dcos,amitaekbote/dcos,dcos/dcos,BenWhitehead/dcos,kensipe/dcos,mellenburg/dcos,dcos/dcos,GoelDeepak/dcos,lingmann/dcos,surdy/dcos,vishnu2kmohan/dcos,asridharan/dcos,mellenburg/dcos,jeid64/dcos,mellenburg/dcos,amitaekbote/dcos,mesosphere-mergebot/mergebot-test-dcos,dcos/dcos,branden/dcos,mesosphere-mergebot/mergebot-test-dcos,mesosphere-mergebot/dcos,BenWhitehead/dcos,asridharan/dcos,BenWhitehead/dcos,GoelDeepak/dcos,darkonie/dcos,GoelDeepak/dcos,mellenburg/dcos,mnaboka/dcos,jeid64/dcos,xinxian0458/dcos,branden/dcos,asridharan/dcos,dcos/dcos,mnaboka/dcos,mnaboka/dcos,amitaekbote/dcos,mesosphere-mergebot/dcos,BenWhitehead/dcos,mesosphere-mergebot/mergebot-test-dcos,kensipe/dcos,kensipe/dcos,darkonie/dcos,xinxian0458/dcos,GoelDeepak/dcos,jeid64/dcos,vishnu2kmohan/dcos,darkonie/dcos,xinxian0458/dcos,jeid64/dcos,branden/dcos