Log which filter failed when on log level INFO

If log level is set to INFO,only see a log message about nova-schedule
attempting to build n instances then a log message about setting the
state to error when the scheduler fails to schedule an instance due to
a filter returning 0 hosts.It may be useful to see which filterreturns 0
host for operator.

Close-bug: #1226334

Change-Id: I7564a8ab093895d1f9db357009aac294783a808b
Merge "Log which filter failed when on log level INFO"