Fix REX-Ray default config
Fix REX-Ray default config

This makes the dcos-rexray service start successfully when no config is
provided during install.

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