Disable datasource matching

[Felipe Jaekel]

Hi,

I noticed that when a datasoure is missing, tomee tries to use another
existing one. I'd like to disable this behavior, so the server will throw
an error.

Motivation: I have a project that uses a mysql and a firebird datasource,
it is hosted by my clients. Recently I had some trouble to figure out that
some weird sql errors were because of incorrect datasource configuration by
the client.

Thanks