Add possibility to create files for testing purpose

[mmichaelis]

In order to enable tests requiring files or directories provide a way to :

• Creates files/directories on the fly.
• Ensures that those files/directories are removed after a test.

This is to fight common anti-patterns like using fixed named resource names and not cleaning up after tests are done. Most tests use temporary files and thus the amount of files in System temp directory increases without end.

References:

• http://commons.apache.org/io/api-release/org/apache/commons/io/FileUtils.html
• http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/io/Files.html