Convert the max_retries argument to integer using native python method int(), instead of the Robot convert_to_integer keyword. This avoid that garbage message is printed to Robot logs as: Argument types are: <type 'unicode'>

Use internal robot builtin method _convert_to_integer in order to avoid unwanted entries in Robot log and output files.

Convert max_retries param to integer using int() casting function in order to avoid unwanted log message and add more meaningful error message if conversion to integer fails. Solution discussed at Pull Request MarketSquare#112 with @bulkan and @oleduc.