Move a couple of methods into a dedicated TestUtils class

Incidentally, this fixes a problem where the temporary directories were
not created in the target/ directory.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Refactor the initialisation of test MavenProjects

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Use simpler way to write pom.xml files for exclusions test

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Move more helpers into TestUtils

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Use static imports

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make sure that transitive dependencies of excluded ones are excluded, too

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a unit test for <dependencyManagement> handling

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>