Time how long select_destinations() takes in conductor
Time how long select_destinations() takes in conductor

When we see weird bugs due to race windows, like bug 1729371,
it would be good to know if we're spending an inordinate amount
of time in the scheduler selecting destinations because that
can have a real effect on things happening before the instance
is created in a cell during the initial create.

Change-Id: I395ac34189c9fc010a37d4a73fac151d0f625ba2
Related-Bug: #1729371

gooddata/openstack-nova,klmitch/nova,openstack/nova,gooddata/openstack-nova,rahulunair/nova,rahulunair/nova,mikalstill/nova,klmitch/nova,openstack/nova,mahak/nova,gooddata/openstack-nova,mikalstill/nova,mikalstill/nova,klmitch/nova,mahak/nova,rahulunair/nova,klmitch/nova,mahak/nova,gooddata/openstack-nova,openstack/nova