[BUILD] Make Intellij IDEA aware of Saros's Git root

Change-Id: I81dccab57f3dcfab238574e5503f38352a979920
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1577
Tested-by: Jenkins CI
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>