SchedulerManager: Check for null demote future and handle double promote
SchedulerManager: Check for null demote future and handle double promote

In the ClientInterfaceRepairCallback.leaderMigrationFailed handle when
there is no future in the map for the partition. Also, in
promotedPartition only call into the handlers if the partition wasn not
already part of the set.

VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb