Support defining mesos slave resources

I set the default to reserve 192mb of ram for non-mesos processes, so
hopefully that is enough.

If you change the resource definitions for a slave and restart it, it
will hang (forever? I don't even know) while trying to recover from the
previous checkpoint.  Thus, this recipe deletes the symlink to the
"last" slave data, which means it will show up as a new slave id when
it comes back.  This may or may not be a good idea - time will tell.

Change-Id: I8cb3691cef34d660c435ffe95d31252988443a06