[test] Added a call to getIJK into test.

This is done to provoke the bug described in pull request #87
[bugfix,parallel] Correctly initialize global_cell in the distributed view.

Previously we erroneously initialized a local variable in function CpGridData::distributeGlobalGrid.
Therefore CpGridData:global_cell_ never contained any entries.

We should of course initialized the class member instead, which is done by this commit.
Make getIJK non-throwing.

As I noticed during the discussion with @andlaus in #87 the CpGrid::globalCell
contains meaningful global values even in the distributed case. Therefore
CpGrid::getIJK will return correct values and there is no reason to throw an
exception, which is removed by this commit.

Beware that the values returned by getIJK cannot be used to access data attached
to the local views of the grid as the indices will be out of bounds of the local
part stored on this processor.

Closes #87.
Merge pull request #88 from blattms/fix_parallel_global_cell

Make getIJK non-throwing and fix parallel globalCell