Avoid clobbering existing tests for SuperLU

We inherited this test from the Dune repositories, but failed to install
sufficient protection in the form of symbol renaming to guarantee that
both tests could coexist.

This issue was exposed by a recent pull request in the OPM-Porsol
repository, namely OPM/opm-porsol#16.
Merge pull request #136 from bska/release-cleanup

Avoid clobbering existing tests for SuperLU