Create unit tests for H5parm

[Joshuaalbert]

Make unittests for:

• Solsets class

• Soltabs class

[tammojan]

For inspiration, you could have a look at the tests of the C++ H5Parm: https://github.com/lofar-astron/DP3/blob/master/DPPP/test/tH5Parm.cc