test_impeswithamg: run the parallel test a bit longer such that something...

test_impeswithamg: run the parallel test a bit longer such that something happens on the second process. Adapt reference solution.

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@11532 2fb0f335-1f38-0410-981e-8018bf24f1b0