Minor refactor tools/releasetools/common.py

- Sort the import modules in alphabetical order.
- Define module variables for avbtool arguments name.

Test: atest releasetools_test
Bug: 300604688
Change-Id: I7990b94cfc1d7b3e977ceb0a3dc2317689891229

tools/releasetools/test_common.py

@@ -1585,7 +1585,8 @@ class CommonUtilsTest(test_utils.ReleaseToolsTestCase):
     info_dict = {}
     cmd = common.GetAvbPartitionArg('system', '/path/to/system.img', info_dict)
     self.assertEqual(
-        ['--include_descriptors_from_image', '/path/to/system.img'], cmd)
+        [common.AVB_ARG_NAME_INCLUDE_DESC_FROM_IMG, '/path/to/system.img'],
+        cmd)
 
   @test_utils.SkipIfExternalToolsUnavailable()
   def test_AppendVBMetaArgsForPartition_vendorAsChainedPartition(self):
@@ -1598,7 +1599,7 @@ class CommonUtilsTest(test_utils.ReleaseToolsTestCase):
     }
     cmd = common.GetAvbPartitionArg('vendor', '/path/to/vendor.img', info_dict)
     self.assertEqual(2, len(cmd))
-    self.assertEqual('--chain_partition', cmd[0])
+    self.assertEqual(common.AVB_ARG_NAME_CHAIN_PARTITION, cmd[0])
     chained_partition_args = cmd[1].split(':')
     self.assertEqual(3, len(chained_partition_args))
     self.assertEqual('vendor', chained_partition_args[0])
@@ -1631,7 +1632,7 @@ class CommonUtilsTest(test_utils.ReleaseToolsTestCase):
     cmd = common.GetAvbPartitionArg(
         'recovery', '/path/to/recovery.img', info_dict)
     self.assertEqual(2, len(cmd))
-    self.assertEqual('--chain_partition', cmd[0])
+    self.assertEqual(common.AVB_ARG_NAME_CHAIN_PARTITION, cmd[0])
     chained_partition_args = cmd[1].split(':')
     self.assertEqual(3, len(chained_partition_args))
     self.assertEqual('recovery', chained_partition_args[0])