tests: qemublock: Add test for raw luks disk format

tests: qemublock: Add test for raw luks disk format

Apart from adding test data add a function which sets up fake secrets
for the test.

The top level disk image would generate the following '-drive' cmdline:

-drive file=/path/luks.img,key-secret=test1-encalias,format=luks,if=none,id=drive-dummy
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>