Accurate exception info in api layer for aggregate

Adjust log information for exceptions in api layer for aggregate
according to
https://wiki.openstack.org/wiki/LoggingStandards#INFO_log_level_is_for_Operators
the LOG.info was removed because nova api already reported error to operator

Change-Id: I89394407495cf2d346e1f532ada236a4364aab24
Merge "Accurate exception info in api layer for aggregate"