add skeleton method for transaction
add skeleton file for transaction tests
make rollback_handler optional
change from lambda to a multi-line function

turns out we need to have processing done in the context of the
function. This solves for that.
fix for pep8 compatibility
limit transaction to nodes
test limiting transactions to nodes
add logging to exception
add init argument for transaction_handler
add documentation for transaction_handler
add test for missing transaction handler
add skeleton for handler
add handler to testcase
handle no handler in transaction call