corrected solver creator for istl solvers and preconditioners

Corrected a bug introduced by MR for coefficient types. The test of the field_type of matrices was replaced.

enabled an automatic merge when the pipeline for 69a7c771 succeeds

added 3 commits

• 69a7c771...ae94a0e6 - 2 commits from branch master
• 5fdb2044 - corrected solver creator for istl solvers and preconditioners

Compare with previous version

merged

mentioned in commit a2ad270c