Add ability to customize volumes-from that get pulled in.

This includes supporting:
  "--volumes-from foo:/some/vol" - which only pulls in "/some/vol"
  instead of all volumes

  "--volumes-from foo:/some/vol:/my/vol" - Provides a custom mount point
  for the pulled in volume

  the :ro :rw options still work and would get tacked onto the end in
  all cases
  This does not break any existing behavior or syntax.

Docker-DCO-1.1-Signed-off-by: Brian Goff <cpuguy83@gmail.com> (github: cpuguy83)