[BUILD] Ignore "bin_test" folders

Change-Id: Idd5983ee5ca3d0126a69e02e8b1f6450a8442f1a
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1419
Tested-by: Jenkins CI
Reviewed-by: Bernd Bieber <brotlee@zedat.fu-berlin.de>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>