Add missing log_format, log_file, log_dir opts.

In 49447c2 we broke keystone in that config.py no longer
provides the options it uses. This commit fixes that
by adding back in conf.log_format, conf.log_file, and conf.log_dir
... all of which are used and required by config.py.

Fixes LP Bug #1122403.

Change-Id: I5015315724eab511f6c570fdd5b9be357777b4a0
Merge "Add missing log_format, log_file, log_dir opts."