vstart: don't set max_mds to use all daemons

vstart: don't set max_mds to use all daemons

This is only useful if you want to test a
single namespace with no standbys.  It's easier
to initially have max_mds=1 and increase it
later than it is to go through the ritual
of decreasing max_mds and then deactivating
a daemon and waiting for it to stop.

Signed-off-by: John Spray <john.spray@redhat.com>