Move systemd logic from Install to Systemd
Move systemd logic from Install to Systemd

* Add Install.systemd attribute
* Add Systemd.manage_systemd_linking()
* Add Systemd.__base_systemd
* Add Systemd.unit_names()
* Add Systemd docstring

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