[Log] Support multiple CLI loggers

[jiasli]

Redo #221

1. Revert cli_logger_name of knack.log.CLILogging.__init__ so that no breaking change is made.
2. Support multiple cli loggers by adding more logger names to knack.log.cli_logger_names list.

[evelyn-ys]

Is it enough when root_logger.handlers is set?
In previous code, both root_logger.handlers and cli_logger.handlers are checked.
Should we check all cli_logger.handlers for cli_logger in cli_loggers?

[jiasli]

Note really necessary, as root logger and cli logger are always set at the same time.

knack/knack/log.py

Lines 171 to 177 in 30592e0

	root_logger.addHandler(_CustomStreamHandler(log_levels['root'],
	log_formats['root'],
	self.cli_ctx.enable_color))
	cli_logger_console_handler = _CustomStreamHandler(log_levels['cli'], log_formats['cli'],
	self.cli_ctx.enable_color)
	for cli_logger in cli_loggers:
	cli_logger.addHandler(cli_logger_console_handler)