Fixed check for unallocated space on disk

So far the check for unallocated space was only working for GPT
and there it was also not really stable. The check was based on
verifying if the backup GPT table is really at the end of the
disk. Depending on which tool was used to dump the image on the
target this "mistake" often got corrected by the tools that
dumped the image. In this case the check no longer worked.
This commit improves the check by another test which looks
for the real free bytes on disk compared to the current
partition geometry.

Author: schaefi

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

@@ -328,7 +328,9 @@ function relocate_gpt_at_end_of_disk {
 
 function disk_has_unallocated_space {
     local disk_device=$1
+    local free_mbytes
     local pt_table_type
+    local end="end of the disk"
     pt_table_type=$(get_partition_table_type "${disk_device}")
     if [ "${pt_table_type}" = "gpt" ];then
         # GPT disks store a backup table at the end of the disk
@@ -337,13 +339,20 @@ function disk_has_unallocated_space {
         # checked and used to detect that there is space
         # unallocated due to a geometry change of the underlying
         # block device layer
-        sgdisk --verify "${disk_device}" 2>&1 | grep -q "end of the disk"
-    else
-        # There is currently no method we could come up with
-        # to detect a geometry change for non GPT based disks.
-        # Thus we assume it's not fully allocated and allow
-        # for resize
+        if sgdisk --verify "${disk_device}" 2>&1 | grep -q "${end}"; then
+            return
+        fi
+    fi
+    # lookup if there is free space on disk compared to
+    # the current geometry values in the partition table
+    free_mbytes=$(
+        sfdisk --list-free "${disk_device}" |\
+            grep -i Unpartitioned | cut -f2 -d, | grep -o -E '[0-9]+'
+    )
+    if [ "${free_mbytes}" != "0" ];then
         true
+    else
+        false
     fi
 }