Don't override the default default_log_level

the default in the sample config is:
default_log_levels=amqp=WARN,amqplib=WARN,boto=WARN,
 qpid=WARN,sqlalchemy=WARN,suds=INFO,iso8601=WARN,
 requests.packages.urllib3.connectionpool=WARN

Using this setting prevents a lot of logging noise eg.
2014-03-07 11:32:13.688 13917 DEBUG iso8601.iso8601 [-] Got u'2014' for 'year' with default None to_int /usr/lib/python2.7/site-packages/iso8601/iso8601.py:124
2014-03-07 11:32:13.688 13917 DEBUG iso8601.iso8601 [-] Got u'03' for 'month' with default None to_int /usr/lib/python2.7/site-packages/iso8601/iso8601.py:124
2014-03-07 11:32:13.688 13917 DEBUG iso8601.iso8601 [-] Got u'07' for 'day' with default None to_int /usr/lib/python2.7/site-packages/iso8601/iso8601.py:124
etc...

Change-Id: I4fdbd3e7a743ad1094f58cc6e7c570ce54933840
Merge "Don't override the default default_log_level"