OFConnectionManager: use AIM_LOG_* directly
OFConnectionManager: remove unused NO_CXN_LOG_VERBOSE macro
OFConnectionManager: remove unused preferred_cxn_id
OFConnectionManager: add an INFO log when a controller connects

Defined as the main connection sending a features reply. I also changed the
existing controller disconnect message to match.
OFConnectionManager: upgrade a couple of logs to WARN
OFConnectionManager: AIM_DIE on memory allocation failures
OFStateManager: fix DPID log statement

It was logging as 32 bits.
OFConnectionManager: tweak log levels

I used a few simple rules:

1. We expect it and it was our fault: ERROR
2. We don't expect it and it was our fault: INTERNAL
3. It wasn't our fault: WARN
4. Not worth going to syslog: VERBOSE
OFConnectionManager: remove unused _TRY macro
OFConnectionManager: remove dead returns after AIM_DIE
OFConnectionManager: don't log at INFO when local controllers connect/disconnect
Merge into master from pull request #166:
OFConnectionManager logging cleanup (https://github.com/floodlight/indigo/pull/166)