After r267897 brought in a new version of file/libmagic, a filesystem image

is identified as "DOS/MBR boot sector" as opposed to "x86 boot sector".

This trips up vmrun.sh when using the new file(1) and makes it want to boot
into the installer instead.

Fix this by just looking for "boot sector" instead.

share/examples/bhyve/vmrun.sh

@@ -176,7 +176,7 @@ virtio_diskdev="$disk_dev0"
 while [ 1 ]; do
 	${BHYVECTL} --vm=${vmname} --destroy > /dev/null 2>&1
 
-	file ${virtio_diskdev} | grep ": x86 boot sector" > /dev/null
+	file ${virtio_diskdev} | grep "boot sector" > /dev/null
 	rc=$?
 	if [ $rc -ne 0 ]; then
 		file ${virtio_diskdev} | grep ": Unix Fast File sys" > /dev/null