Fix various issues with initial setup/restart.

Some experimentation led to the realization that Vagrant's customizations
aren't executed directly, they're stored for *possible* later execution.  So
any conditions used in the Vagrantfile must be based on things that happen as
a consequence of running a customization.

In the case of storage controllers, there is no way for us in a Vagrantfile
to know whether it exists at the time the customizations are created.  So,
link it to the creation of the first disk.  There's already a race between
creating the disks and adding them, so this is ok.

Finally, remove the begin..rescue..end blocks.  Since the executions are
delayed from the Vagrantfile, these blocks have no effect.

This change fixes the initial setup vs machine restart problem.