Test base/hdf5_03.mpirun={1,4}: do not compare test output

Test base/hdf5_03.mpirun={1,4}: do not compare test output

We have been adding output variants for this test for years, but the
test output is simply not stable. I see different output depending on
debug or release configuration and chosen optimization level.

Let us stop here and only check whether the test runs correctly without
throwing an exception.