avocado.cli.parser: New way to parsing arguments.

* Modify how we parse command line arguments, by removing the logic that was inside avocado.cli.app into this new module.
* On Plugin.configure(), remove app_parser and cmd_parser arguments and now use parse, an instance of avocado.cli.parser.Parser(). The application (old app_parser) is available with parser.application. The subcommands (old cmd_parser) is available with parser.subcommands.
* Now the runner plugins (like sysinfo, datadir, run, etc.) make use of the standard method run() to execute the logic.
* Remove generic option --silent and turn it to subcommand run.
* The parser for the subcommand run now accepts one or more tests ids (paths / aliases) and there isn't a need to quote the list as a string.