Ensure JUnit & TestNG tests run in spring-test

Prior to this commit, the Gradle build configuration only executed
TestNG-based tests and effectively disabled all JUnit-based tests in the
spring-test module. Furthermore, TestNG-based tests were not properly
reported in Bamboo CI builds.

This commit ensures that both JUnit and TestNG tests are executed in the
Gradle build by defining a new testNG task within the spring-test
configuration. The test task now depends on the new testNG task.
Furthermore, the testNG task makes use of Gradle 1.3's support for
generating test reports for TestNG tests alongside reports for JUnit
tests. The net effect is that all tests are executed and reportedly
properly in Bamboo builds on the CI server.

- Enabled both JUnit and TestNG tests for the spring-test module.
- Corrected bugs in FailingBeforeAndAfterMethodsTests introduced in
  commit 3d1b3868fe3b38f5552883f54111c53f6ee75572.
- Deleted the now obsolete SPR-9398.txt file.

Issue: SPR-9398