Fix scrubber and other utils to use log.setup().

scrubber and other utils call config.setup_logging(),
which does not read the 'default_log_levels' config option.
Fix this problem by calling log.setup(), just like what
glance-api and glance-registry do.

Per John Bresnahan's comment, made the change to check
the existence of log conf file in oslo-incubator code.
Refer to https://review.openstack.org/#/c/24230/

Change-Id: I4a53d74c4cd8274a3174b246207a6ed76c5e31c6
Fixes: bug #1153432
Merge "Fix scrubber and other utils to use log.setup()."