cros_update: Prepare to move to chromite

Also cleanup the python3 migration requirements.

Cleanup argument generation logic. It was quite dirty.

BUG=chromium:1003986
TEST=devserver_integration_test.py

Change-Id: Ieb360fc3d3643211545b8b0a1a7f06d365b64fb1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/1865147
Tested-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/cros_update_progress.py b/cros_update_progress.py
index 9bcb906..0a7d5c3 100644
--- a/cros_update_progress.py
+++ b/cros_update_progress.py
@@ -29,13 +29,8 @@
 
 import log_util
 
-# only import setup_chromite before chromite import.
 import setup_chromite  # pylint: disable=unused-import
-try:
-  from chromite.lib import osutils
-except ImportError as e:
-  _Log('chromite cannot be imported: %r', e)
-  osutils = None
+from chromite.lib import osutils
 
 # Module-local log function.
 def _Log(message, *args):