acm: Provide the possibility to choose the VM label of domain-0 in the

acm: Provide the possibility to choose the VM label of domain-0 in the
kernel line in grub.conf. The format is
ssidref=<ssidref>:sHype:<policy name>:<vm label>. The name of the
policy specified here must be the same name as the in the policy
provided as a module during boot, otherwise the policy will not be
accepted and the system then starts without a policy. The user tool
for 'xm dumppolicy' has been adapted to show which entry in the binary
policy is used by domain-0.

Signed-off-by: Stefan Berger <stefanb@us.ibm.com>