Run LoaderIntegrationTests against multiple JDKs

[philwebb]

LoaderIntegrationTests is currently pegged to JDK 15, It would be nice to run against 8, 11 and 17 and possibly a few different JRE vendors.

[wilkinsona]

Re-opening as LoaderIntegrationTests need to be disabled when Docker isn't available (@DisabledIfDockerUnavailable).