dcos_installer/action_lib: remove SELinux from install-prereqs
dcos_installer/action_lib: remove SELinux from install-prereqs

GoelDeepak/dcos,surdy/dcos,mesosphere-mergebot/mergebot-test-dcos,dcos/dcos,surdy/dcos,kensipe/dcos,GoelDeepak/dcos,surdy/dcos,kensipe/dcos,mesosphere-mergebot/dcos,kensipe/dcos,dcos/dcos,surdy/dcos,GoelDeepak/dcos,dcos/dcos,kensipe/dcos,mesosphere-mergebot/dcos,mesosphere-mergebot/mergebot-test-dcos,GoelDeepak/dcos,mesosphere-mergebot/dcos,mesosphere-mergebot/mergebot-test-dcos,mesosphere-mergebot/mergebot-test-dcos,mesosphere-mergebot/dcos,dcos/dcos,dcos/dcos