No warning when filters are given as a comma-separated list instead of a pipe-separated list

A lack of caffeine resulted in me using filters=filter1,filter2 in my configuration and the error was that the filter filter1,filter2 wasn't found. This is of course obvious once I realize I used the wrong delimiter but for someone who's not familiar, this isn't necessarily obvious.

For comma-separated as well as space separated lists, MaxScale should log a helpful warning if the filter list looks valid but uses the wrong delimiter.