Connection Manager should have the ability handle connection specific args

Currently, each SqoopTool has and init(SqoopOptions)/validateOptions(SqoopOptions) calls that gives each too the ability to parse, validate and add options to SqoopOptions. Ideally there would be a similar generic mechanism for handling args for ConnectionManager-specific settings. (Mysql settings, postgres settings, etc). Furthermore, this mechanism should allow for plugin loaded ConnectionManagers to have its own args handler and options that are not part of the core sqoop system.