assembler/qemu/grub: don't search for the root partition

We know the root partition we want, as we are setting it up. There
is no need to search for it by filesystem UUID. This simplifies the
setup and means the level 1.5 bootloader is always the same, and
not dependent on an embedded UUID.

Signed-off-by: Tom Gundersen <teg@jklm.no>

assemblers/org.osbuild.qemu

@@ -36,7 +36,6 @@ def main(tree, output_dir, options, loop_client):
 
     image = f"/var/tmp/osbuild-image.raw"
     grub2_core = "/var/tmp/grub2-core.img"
-    grub2_load = "/var/tmp/grub2-load.cfg"
     mountpoint = f"/tmp/osbuild-mnt"
 
     # Create an empty image file
@@ -52,10 +51,6 @@ def main(tree, output_dir, options, loop_client):
     partition_offset = partition["start"] * 512
     partition_size = partition["size"] * 512
 
-    with open(grub2_load, "w") as load:
-        load.write(f"search.fs_uuid {root_fs_uuid} root \n"
-                   "set prefix=($root)'/boot/grub2'\n")
-
     # Create the level-2 bootloader
     # The purpose of this is to find the grub modules and configuration
     # to be able to start the level-3 bootloader. It contains the modules
@@ -63,12 +58,11 @@ def main(tree, output_dir, options, loop_client):
     subprocess.run(["grub2-mkimage",
                     "--verbose",
                     "--directory", "/usr/lib/grub/i386-pc",
-                    "--prefix", "/boot/grub2",
+                    "--prefix", "(,msdos1)/boot/grub2",
                     "--format", "i386-pc",
                     "--compression", "auto",
-                    "--config", grub2_load,
                     "--output", grub2_core,
-                    "part_msdos", "ext2", "biosdisk", "search_fs_uuid"],
+                    "part_msdos", "ext2", "biosdisk"],
                    check=True)
 
     assert os.path.getsize(grub2_core) < partition_offset - 512