Shorten shear wave scenario.

The shear wave scenario had too long a runtime for the nightly tests.
This merge request reduces the number of time steps per run and restricts the scenario to one resolution and viscosity. The variation in LBM models is maintained.
These measures reduce the runtime of the entire study to approx. 4 minutes.

requested review from @holzer

assigned to @schottenhamml

changed the description

approved this merge request

merged

mentioned in commit 358eead3