GRADLE-2957 Dependent tasks with same finalizer

Based on discussions around the [GRADLE-2957](https://issues.gradle.org/browse/GRADLE-2957) defect, a test can be designed to reproduce the case where a tree of dependent tasks share the same finaliser. In this case, the detection of cycles does not seem to work properly.

In my commit, I have chosen to by-pass the wrong cycle detection and go on with the execution plan creation.