cros: hoist option freezing to common code

Now that all the options mutation logic is pulled out into a dedicated
step (ProcessOptions), we can enforce option freezing in common code.
Then we can delete the explicit calls that most of the commands were
already doing.

BUG=b:187789324
TEST=CQ passes

Change-Id: I70acdab83c2245e107b3cb9551523266403634a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3346744
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Alex Klein <saklein@chromium.org>
diff --git a/scripts/cros.py b/scripts/cros.py
index 54025be..5530157 100644
--- a/scripts/cros.py
+++ b/scripts/cros.py
@@ -87,6 +87,7 @@
     namespace = parser.parse_args(argv)
     namespace.command_class.ProcessOptions(parser, namespace)
     subcommand = namespace.command_class(namespace)
+    namespace.Freeze()
     try:
       code = _RunSubCommand(subcommand)
     except (commandline.ChrootRequiredError, commandline.ExecRequiredError):