refactored mixins - disambiguated db exceptions

renamed a lot of things that called database and connection with the hopes of disambiguating them.

At the same time, I realize that  the TransactionExecutor would reset the connection for any exception even if that exception had nothing to do with the connection.  As a temporary fix I catch the exceptions from dbapi2_util class and don't reset the connection if those are detected.  This needs a better fix and the fix should also propagate to Socorro. 

In Socorro, the problem doesn't hurt us because PGBouncer hides the connects/disconnects