tests: junit_tests.sh:

- Enable assertions for JVM.
- Create test directory and the subdirectory log if they do not exist.
- Guess XTREEMFS directory if $1 was omitted.
- Do not log the whole command line for compiling the tests because it is far too long.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@3546 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534