Fixed resize of dos table type on s390

On s390, parted is used to detect the partition table type.
In contrast to blkid the name for DOS tables is reported
as 'msdos' and not 'dos' which impacts several conditions
in the kiwi initrd code which checks for 'dos'. This commit
fixes the get_partition_table_type() method to return a
consistent table name for DOS tables. This Fixes bsc#1228729

dracut/modules.d/99kiwi-lib/kiwi-partitions-lib.sh

@@ -290,11 +290,22 @@ function get_free_disk_bytes {
 
 function get_partition_table_type {
     local disk_device="$1"
+    local table_type
 
     # blkid doesn't work for dasd partitions, so on s390 parted is used
     # to detect the partition type (bsc#1209247)
     if [[ "$(uname -m)" =~ s390 ]];then
-        parted --script --machine "${disk_device}" print | grep "^${disk_device}" | cut -d":" -f6
+        table_type=$(
+            parted --script --machine "${disk_device}" print |\
+                grep "^${disk_device}" | cut -d":" -f6
+        )
+        if [ "${table_type}" = "msdos" ];then
+            # make sure to set a consistent table name for the
+            # DOS table type. In the initrd code we use 'dos'
+            # as identifier but parted reports msdos
+            table_type="dos"
+        fi
+        echo "${table_type}"
     else
         blkid -s PTTYPE -o value "$disk_device"
     fi