rename local trace module

There is a standard Python "trace" module, so having a local trace.py
prevents us being able to import that.  Rename the module to avoid.

Change-Id: I23e29ec95a2204bb168a641323d05e76968d9b57
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/234832
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Mike Frysinger <vapier@google.com>

progress.py

@@ -17,7 +17,7 @@
 import os
 import sys
 from time import time
-from trace import IsTrace
+from repo_trace import IsTrace
 
 _NOT_TTY = not os.isatty(2)