Test with Debezium's "connect-base" image rather than "connect"

[gunnarmorling]

This should speed up things a bit, as scanning the plug-in path takes quite some time for the Debezium image with all its connectors and SMTs. This will require adjustment of a small number of tests though which expect the Debezium connector plug-ins to be available.

[C0urante]

Hey look @gharris1727, I found another reason to speed up plugin loading in Connect!

@gunnarmorling One thing I'd want to make sure of is that there's still at least one connector present in the image, so that we can still test things like get plugins. IIUC the base image has the MM2 connectors on it, so this seems fine 👍

[gunnarmorling]

Yes, exactly, the MM2 connector is there, we use it for some tests already.

[gunnarmorling]

The correct name of the image is "connect-base" btw, just updated the issue title accordingly. It's available on quay.io and DockerHub, I'd suggest to go with the former, as it's the primary publication target for the project nowadays, i.e. quay.io/debezium/connect-base.