Add debug log for availability zone filter

Sometimes operator need information why the host doesn't pass
the check of scheduler, this patch adds information for available
zone filter if the host doesn't belong to required available zone
and modify the logic a little to make it less nested.

Change-Id: Icb45182fa58d69e7c5e3a77ea31eddc492ac46ec
Partial-Bug: #1301830
Merge "Add debug log for availability zone filter"