Update tests to work with new implementation.
Update tests to work with new implementation.

Had lots of issues surrounding Ifg objects being opened then passed to estimate_ref_phase causing segfaults. It seems best in future to close the Ifg object after calling the 'preparation' method so the changes to the underlying GDAL dataset are saved and then just passing the Ifg paths to estimate_ref_phase.

GeoscienceAustralia/PyRate,GeoscienceAustralia/PyRate