LP #1256400: pt-stalk should support RDS

**Reported in Launchpad by Fernando Ipar last update 17-08-2017 19:21:07

This is a feature request.

I think pt-stalk should support a degraded mode for RDS.
It does not have teo be automatic, maybe just include an option --mysql-only (or whatever name makes sense), to only trigger the mysql captures (innodb status, processlist, etc) and nothing that depends on filesystem access (including the error log).