[linearelliptic.testcases...] add H_with_h (default to false)
[linearelliptic.testcases...] add H_with_h (default to false)

This allows to run a multiscale test case where coarse and fine grid are
refined, such that H/h is constant.

tobiasleibner/dune-hdd,tobiasleibner/dune-hdd