Fix test setup for Eclipse Photon and greater

Fix test setup for Eclipse Photon and greater

When a source folder is marked as a test folder, JDT requires that it
has an output folder different from the one used for regular sources.
Therefore give the test folders in org.eclipse.jgit.test a separate
output folder "bin-tst".

Moreover JDT reports errors if non-test classes have dependencies on
test classes. Therefore remove the "test" annotation from
org.eclipse.jgit.junit.

Change-Id: Ib527439ff5b7d7b570b8a60819ecaa70f59c63a3
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>