Allow for missing storage-aggregation.conf.
Add import, catch IOError too.
Merge pull request #93 from mblair/fix-for-missing-storage-aggregation-conf

Allow for missing storage-aggregation.conf.
add a config option to turn off logging of successful connections

this patch adds a config option which can be added for the
cache/relay/aggregator instances to not log successful connections anymore.
For this the config option LOG_LISTENER_CONN_SUCCESS has to be set to False.