ROMSpline fields of Format 2 and 3 are incorrectly vaildated

The current builds validation for ROMSpline fields checks that each subfield of this h5.Group contains the subfields listed in the format specification.

It should actually check that subfields (X, Y, deg, error, tol) are present (those output by romSpline) where X and Y represent the two fields (t_horizon, <variable>) as defined in the format specification.

Please see https://sympa.ligo.org/wws/arc/cbc/2016-12/msg00135.html for more details.