Clean up extra modules code

The config generator extra modules code was attempting to look up
an empty module name if extra modules were not specified.  This
resulted in a spurious exception.

This change also strips the module names so extra spaces in the
env var won't cause problems.

Change-Id: I4cfbeb62fc25220ab43d6f80006245be3376dc93
Improve error reporting on import failures

The existing config generator code does not report general errors
importing modules well.  In my case, that meant I had no idea that
an old version of six on my system was causing a module import to
fail.

This change logs all errors importing a module to stderr.

Change-Id: I4663f5bbd4f553c0d6ce5f84b1c1275a7304e3b5
Merge "Clean up extra modules code"
Merge "Improve error reporting on import failures"