ioemu: strip tap subtype prefix from image name

ioemu: strip tap subtype prefix from image name

Currently I am not able to mount or boot from an HVM CDROM when it is
configured for 'tap:aio' instead of 'file'.

disk=[ 'tap:aio:/var/lib/xen/images/sles10-sp2-fv/disk0,hda,w', '
       tap:aio:/home/iso/sles/SLES10.iso,hdc:cdrom,r', ]

With this patch I am able to boot from the CDROM and or mount it.

Patch changes xenstore.c:xenstore_process_event() to strip the tap
subtype prefix from the image name.

Signed-off-by: Pat Campbell <plc@novell.com>