Reduce logging in scheduler

The logging in the scheduler is what takes most of the time,
once you are doing no DB calls.

This ensures the servicegroup is_up and retry_filter only log
on failures, which is more in line with the other filters.

Using the test "test_performance_check_select_destination"
modifying it to use 200 hosts, the request time went from
70ms to under 10ms.

We could reduce logging further, but this minimal change makes
a massive impact. The next steps would require a config value
to disable all debug logging in the scheduler.

Closes-Bug: #1301515

Change-Id: Ia4c7e506e8df9c560c349e2ebec3f5111aa0cb0d
Merge "Reduce logging in scheduler"
Merge commit 'refs/changes/38/84138/2' of git://gold.eng.hq.xensource.com/git/github/openstack/nova into tmpbranch