Make ordering of Lustre targets "Optional" (as opposed to "Mandatory").

See email by Robert Read to hpdd-discuss on May 23, 2014:

> The strict ordering of MGT, MDT, OST is only a hard requirement for
> the very first start of the file system, because the targets need to
> compete the initial registration with the MGT before they can be
> used.  Subsequent cold restarts of the filesystem don’t necessarily
> need to start any particular order, but it’s still not a bad idea to
> start MGT first since all the servers will attempt to connect to it
> when they start, though they should start without it eventually.