Fix auth_token.py bad signing_dir log message

Fixes bug 1197755

Change-Id: I16152518c354821af6790a6e459f1d8ec09139a0
Flake8 should ignore build folder

This adds 'build' to the exclude list for flake8

Fixes bug 1198329

Change-Id: Ia3688a2fc0334d32d89f04d114242d39bdc25f0e