container: Fix resizing disk image containing multiple partitions

Closes: #2324.

The arm64 image contains two partitions in a GPT partition table. First is the
EFI partition and the second is the root partition. The container script
currently assumes that there will only be one partition in the image file. Fix
this by picking up the partition number of the last partition and resizing that.
GPT partition table also requires relocating the second copy of the partition
table to the end before partition resize can succeed.

Tests:

- Create testing containers in arm64 and amd64 architectures.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

container

@@ -368,6 +368,7 @@ def _verify_dependencies():
         'gpg': 'gpg',
         'xz': 'xz-utils',
         'parted': 'parted',
+        'sgdisk': 'gdisk',
         'btrfs': 'btrfs-progs',
         'nmcli': 'network-manager',
         'ssh': 'openssh-client',
@@ -522,6 +523,21 @@ def _download_disk_image(distribution, force=False):
     return _extract_image(target_file)
 
 
+def _get_partition_info(image_file):
+    """Return the number of the final partition in the image file."""
+    process = subprocess.run(
+        ['sudo', 'parted', '--script',
+         str(image_file), 'print'], stdout=subprocess.PIPE, check=True)
+    lines = process.stdout.decode().splitlines()
+    last_partition_number = lines[-2].split()[0]
+    partition_table_type = 'msdos'
+    for line in lines:
+        if line.startswith('Partition Table:'):
+            partition_table_type = line.partition(': ')[2]
+
+    return partition_table_type, last_partition_number
+
+
 def _resize_disk_image(image_file, new_size):
     """Resize the disk image if has not already been."""
     if new_size[-1] != 'G':
@@ -542,14 +558,22 @@ def _resize_disk_image(image_file, new_size):
         ['truncate', '--size',
          str(new_size_bytes),
          str(image_file)], check=True)
+    partition_table_type, last_partition_number = _get_partition_info(
+        image_file)
+    if partition_table_type == 'gpt':
+        subprocess.run(
+            ['sudo', 'sgdisk', '--move-second-header',
+             str(image_file)], check=True)
+
     subprocess.run([
         'sudo', 'parted', '--align=optimal', '--script',
-        str(image_file), 'resizepart', '1', '100%'
+        str(image_file), 'resizepart', last_partition_number, '100%'
     ], check=True)
     process = subprocess.run(
         ['sudo', 'kpartx', '-avs', str(image_file)], stdout=subprocess.PIPE,
         check=True)
-    partition = '/dev/mapper/' + process.stdout.decode().split()[2]
+    last_line = process.stdout.decode().splitlines()[-1]
+    partition = '/dev/mapper/' + last_line.split()[2]
     subprocess.run(['sudo', 'btrfstune', '-uf', partition], check=True)
 
     with tempfile.TemporaryDirectory(