Clean help flags

in the case of the zk flag.  the help is wrong.  The full file:/// protocol **must** be followed.  the way it is written, it appears as though you can just provide the absolute path, which fails.

The rest of it, cleans up the help to be more consistent with the phrasing.
I'm not sure that /tmp/mesos is the best example for this as it implies that it is ok for the data to be wiped when /tmp is cleaned by the OS.