Explicit file descriptor limits for all DC/OS services

Of all the DC/OS services, only spartan and mesos-master,mesos-slave,mesos-public-slave set file limits. In all other cases the limit defaults to whatever is the default for the distribution. In the case of CoreOS the default soft limit is 1024.

We should specify sane open file limits for all DC/OS services. We should start out with something pretty big and decrease it as we collect statistics from large, busy clusters.