londiste.handlers: removed duplicate debug logging
simple retriable execute (for sql)

the idea is that db calls occasionally break due to transient issues and we’d rather have the calls retried before raising exceptions etc
another iteration from past
made more robust, returns retry count and valid cursor
cleaned up, even more robust, added logging, feature inactive by default
Merge branch 'feature/retriable_execute' into develop
skytools.scripting: added options to lower log level for exceptions

The idea is to suppress error level log messages for a grace period
in order not to pollute logs with transient errors that nobody would act upon.