Issue reported in the forums: https://discuss.gradle.org/t/2-14-unexpected-servlet-api-classes-on-plugin-test-classpath/18943/2

Basically I think our shading strategy is too wide when it excludes all classes starting with `javax`: servlet-api (but probably the only example) provides classes in this package, so we should remove the exclude and replace it with a better, per-package exclude. However this might be complicated to do (how to generate that list, and how to make sure we don't break something else?).

Alternatively, we can have a "force" list to re-include after exclusion.