Updated automatic install:

* Reboot prompt was still displayed due to faulty handling of default
* Better logic to wait for XAPI to be running.

NOTE: I have not been able to test this, I believe due to an existing bug
where XAPI is never ready because it's not running under Xen.
This patch may be irrelevant depending on the fix identified for running XAPI
and how the xe commands will be run, but I was asked to share it anyway