Change to cassandra.py so that when setting nodes the pool is cleared.  This caused me massive pain when I loaded one Service, then another in the same python session, hence the compute nodes got initialized in the WRONG database!
Change to cassandra.py so that when setting nodes the pool is cleared.  This caused me massive pain when I loaded one Service, then another in the same python session, hence the compute nodes got initialized in the WRONG database!

tscholl2/smc,sagemathinc/smc,sagemathinc/smc,DrXyzzy/smc,sagemathinc/smc,DrXyzzy/smc,tscholl2/smc,DrXyzzy/smc,sagemathinc/smc,tscholl2/smc,tscholl2/smc,DrXyzzy/smc,tscholl2/smc