Add test dependency on logback
Run tests in headless mode
Remove unneeded @BeforeClass methods
Remove test bundle activator
Store temp test data in target/ instead of /tmp/
Allow customizing installation repositories

For testing it is necessary to be able to customize repositories from
which dependencies will be resolved.
Use separate mock root for testing installer
Add dependency version installer tests
Simplify expectation declarations in installer test
Add tests for OSGi requires generator