change warn to notice for connection drop & half

closed
logwarn -> notice for line length exceeds msg
connection: connection error warn -> notice

If Haraka is behind HAproxy, with TCP checks enabled, it will log many, many
of these warnings, and they aren't really 'errors' per se. NOTICE should be
plenty of priority.
connection: lognotice -> info (per @smf)
Merge pull request #663 from msimerson/connection

Connection