Custommize mountdisks.BASE as well

Also use parted to get the offset and size of the partitions in bytes.
We need to know the size of the root partition (not just its offset)
because the end of the disk is gpt.

Bug: N/A
Test: cd package/modules/Virtualization/build/debian &&
sudo docker run -v $(pwd):/root/git --privileged -it ubuntu::22.04
bash /root/git/build.sh

Change-Id: Ic4367ff7fd8555ee89735e0cc1cd7f98ca5b41ff
diff --git a/build/debian/build.sh b/build/debian/build.sh
index 24de78a..4d59981 100755
--- a/build/debian/build.sh
+++ b/build/debian/build.sh
@@ -106,3 +106,4 @@
 download_debian_cloud_image
 copy_android_config
 run_fai
+fdisk -l image.raw