5.1 build fix for JUnit based validation of pull requests

The first commit  fixes some sample reports to use an in-memory database instead of a file-based HSQL database to avoid random test-failures due to concurrent accesses to the same database when tests run in parallel. 

The second commit updates some of the build files to ensure that the project can be build and tested without using cobertura. Cobertura is unable to cope with large code bases and slows down the tests by a factor of 2 to 3. To validate pull requests, we are interested in finding test failures and a pure JUnit run does the job in about 1 hour. 

With this patch in place the complete project can be validated via "ant continuous-local-junit" followed by the longrun tests of engine/core and engine/testcases (via "ant longrun-test").