Use sync mode in kparx when mapping partitions

Pass -s flag to kpartx to fix a potential race condition when deploying
(ext|ntfs)dump images. Without -s, kpartx will return right after
signaling the device mapper to create the partition block devices. This
does not guarantee that the partitions will have been created when
snf-image will try to use them.

snf-image-host/common.sh.in

@@ -189,7 +189,7 @@ get_api20_arguments() {
 
 map_disk0() {
     blockdev="$1"
-    filesystem_dev_base=$($KPARTX -l -p- $blockdev | \
+    filesystem_dev_base=$($KPARTX -l -s -p- $blockdev | \
                             grep -m 1 -- "-1.*$blockdev" | \
                             $AWK '{print $1}')
     if [ -z "$filesystem_dev_base" ]; then