OfOverlayRendererTests overlaps with other Unit tests

Please notice line 84 in OfOverlayRendererTests: https://git.opendaylight.org/gerrit/#/c/24153/

when(config.getGbpOfoverlayTableOffset()).thenReturn(null);

It was added, because some other unknown test leaves SwitchManager in an odd state.

How to reproduce: remove line 84 and run all the tests (/src/test/java)

If you can't reproduce or you don't see an error message in your IDE, try to build OF-Overlay Renderer with Maven. (clean install)

Error message:
http://pastebin.com/BVB1JKtB

Note: if you run just OfOverlayRendererTests, it will run successfully.

Please, verify in master and stable/lithium as well.