The ssh_node function now supports printf style arguments. This is used to
simplify command execution on the nodes.
Curreltny, in addition to its old usage, it is used to drop extra
databases when replication is started.
The test attempted to copy the generated CSV file from the MaxScale server
when in fact it was on the master server. Removed HEAVY label from the
test as it takes about 10 seconds to run.
Cherry-picked from commit f80cde2af149fda9c47d8f9131f82527b76af487.
