[RFC] Change nonbonded-fep-test reference data to analytical Ewald

[RFC] Change nonbonded-fep-test reference data to analytical Ewald

The nonbonded-fep-test reference data for Ewald type interactions
was generated using tabulated interactions. There have a max error
of 0.1*ewald_trol=1e-6. In preparation for the switch to analytical
corrections, the reference data is now generated with analytical
corrections. The required a tolerance in double precision of 1e-6.