fix opm-parser find rule

deals with the fallout of opm-parser #365 and #366
Merge pull request #236 from akva2/fix_opmparser

fix opm-parser find rule
[bugfix] use SparseLU when UMFPack was not found.
Merge pull request #238 from dr-robertk/PR/sparselu-when-no-umfpack

[bugfix] use SparseLU when UMFPack was not found.
Merge remote-tracking branch 'upstream/master' into autodiffdune