Change DEBUG log in loopingcall to TRACE level log
Change DEBUG log in loopingcall to TRACE level log

The DEBUG log message in _run_loop() method will record every
loopingcall info every interval, that may cause log noise. e.g. In
ceilometer, the partition coordinator will have a fixed interval looping
call every two seconds as default.

Change-Id: I32aa474ece2458aa7cc1a5c271a40f664bf07af2

poznyakandrey/oslo.service,openstack/oslo.service