Gradle: inject test resources before the main resources for testing

[aloubyansky]

Fixes #8845
Fixes #8901

[aloubyansky]

Hm, I noticed a difference in how I implemented this for Gradle vs how it seems to work for Maven currently.
In Maven, application.properties from the test resources dir seems to replace the main application.properties.
While in Gradle (in this PR) application.properties from the test resources is added a dominating config source.
So, we need to decide what's more appropriate. I tend to prefer the way it's implemented in this PR. However, it'll be a breaking change.

[aloubyansky]

I should probably re-work it so the main application.properties is completely replaced with the one from the test. Partial overrides are supported using profiles.

[aloubyansky]

Ok, I've re-worked it to replace the main application.properties

[geoand]

Thanks!

[mklueh]

Does that mean it'll replace the entire file contents so you have to have your whole production application properties duplicated if you just want to change one single property for your tests? I was always under the impression that it is kind of merged and the test properties that are defined will overwrite those that are given in the main application.properties

[aloubyansky]

Yes, it is completely replaced. We thought that with profiles you already have a way to override properties selectively. And it is also consistent with how it works in Maven.