CloudWatch logs config: define multi_line_start_pattern

[pasha-r]

Right now multi_line_start_pattern can only be the default one. Sometimes it'd be a nice feature to gather traceback lines into a single log message.

My feature request is this change to the config syntax:

cloudwatch_logs:
  /var/log/syslog:
    log_group: my-syslog-loggroup
    multi_line_start_pattern: '^[^\s]+'

multi_line_start_pattern is optional, if it's not there, there will be no multi_line_start_pattern in the resulting awslogs.conf file