c-s CLI: support `-errors` option

[muzarski]

As mentioned in #64, the config's max_retries_per_op is now hardcoded to 9 (c-s default value).

In c-s, this value can be adjusted by the user with -errors retries= CLI parameter.

The solution is to simply extend CLI by -errors option which introduces retries= as well as other additional parameters related to cql-stress error handling.