Ensure that when no box is defined for a pxe install, that the domain
name is only populated for subsequent boots and if it is already
provided by a create action, skip attempting to retrieve from a
non-existing domain XML.
Fixes: #1508
With multi volume boxes, need to ensure that disk settings such as the
device assigned are resolved dynamically once it has been established
which devices have already been assigned to the box volumes on either
initial creation or subsequent boots.
Otherwise users are forced to always explicitly define the device for
additional storage instead of having it be automatically assigned the
next available device.
Consequently previous changes have broken the ability for machines
with additional storage to be halted and restarted correctly.
Include an integration test that for additional storage checks that the
machine can be stopped and started again.
Fixes: #1490
