Add code to read the suse specific suse-diskcache-disable-flush flag out
of xenstore, and set the equivalent flag within QEMU.
Patch taken from Xen's patch queue, Olaf Hering being the original author.
[bsc#879425]
[BR: minor edits to pass qemu's checkpatch script]
[BR: With qdevification of xen-block, code has changed significantly]
Signed-off-by: Bruce Rogers <brogers@suse.com>
Signed-off-by: Olaf Hering <olaf@aepfle.de>