Fix in bpttool make_disk_image subcommand

Change-Id: Ic69cc178d2b080b465d5e593b2fb16a0d4901696
diff --git a/bpttool b/bpttool
index 3e57695..6b4f56d 100755
--- a/bpttool
+++ b/bpttool
@@ -1028,7 +1028,7 @@
                             action='append')
     sub_parser.add_argument('--allow_empty_partitions',
                             help='Allow skipping partitions in bpt file.',
-                            action='store_false')
+                            action='store_true')
     sub_parser.set_defaults(func=self.make_disk_image)
 
     sub_parser = subparsers.add_parser(