Allow passing arguments with -- in addition to -.

This allows the Unix-like command-line argument --show.  We keep the
existing -show.

Test: get_rust_pkg.py -show foo
Test: get_rust_pkg.py --show foo
Change-Id: I5906e0c59ef6f9e4ad33b0a9645a1fc4d9d9e1aa

scripts/get_rust_pkg.py

@@ -57,7 +57,7 @@ def parse_args():
   parser.add_argument(
       "-o", metavar="out_dir", default=".", help="output directory")
   parser.add_argument(
-      "-show",
+      "-show", "--show",
       action="store_true",
       default=False,
       help="show all default dependent packages, using crates.io api")