s390-bios: Skip bootmap signature entries

s390-bios: Skip bootmap signature entries

Newer versions of zipl have the ability to write signature entries to the boot
script for secure boot. We don't yet support secure boot, but we need to skip
over signature entries while reading the boot script in order to maintain our
ability to boot guest operating systems that have a secure bootloader.

Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Message-Id: <1556543381-12671-1-git-send-email-jjherne@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>