Run dask+SGE backend without SETSHELL = starvation

It's being a while we have this issue, but I've never materialized it here.

When a script that uses dask+SGE backend is executed at Idiap without a SETSHELL grid, the script hangs forever waiting for a worker. We need to, i-) either throw an exception once qsub fails to be executed or ii-) do like it's done in gridtk (triggers this automatically).