security: AppArmor allow write when os loader readonly=no

security: AppArmor allow write when os loader readonly=no

Since libvirt commit 3ef9b51b10e52886e8fe8d75e36d0714957616b7,
the pflash storage for the os loader file follows its read-only flag,
and qemu tries to open the file for writing if set so.

This patches virt-aa-helper to generate the VM's AppArmor rules
that allow this, using the same domain definition flag and default.

Signed-off-by: Miroslav Los <mirlos@cisco.com>
Tested-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>