Log last compute error when rescheduling.
Log last compute error when rescheduling.

When a scheduling attempt is re-tried, log the last exception from
the compute side.  The goal is to provide simpler access to debugging
information about why a build/resize is having issues.

Change-Id: Ic31852dcbbf1cea9034a4b8eb1c7d20178c3229d

n0ano/gantt,n0ano/gantt