Support for "preboot ACL"s

Created by: gicmo

Kernel change (docu)

Todo:

• new BoltAuthFlag: BOLT_AUTH_BOOTACL to indicate the device is in the boot access control list
• expose the boot_acl attribute of the domain
• check if boot acl is in sync on startup (maybe auto-sync?)
• when a domain comes online, set the bootacl flag of devices in the domain's boot acl

Maybe:

• DBus API to include a device in the boot acl (one idea: make authflags writeable), needs the domains to be online
• DBus API to add, remove device from all boot acls