xapi: before a reboot, make sure to flush the database

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #42 from djs55/sync-database

xapi: before a reboot, make sure to flush the database
Merge pull request #43 from jamesbulpin/master

Two small fixes to make xenserver-install-wizard work on a CentOS Live CD