fehmpytests fails for cellbased

This seems to be an issue with how python compares the output files.
The output is fehmn.out which has a format that is tricky to compare.
We need to determine which portion of the file should be evaluated, and ignore the rest of the file.

Though very different, the end of the files compare the same:
es19:% ll /.out
-rw-rw---- 1 tamiller sft 157974 Aug 20 11:08 compare/fehmn.out
-rw-rw---- 1 tamiller sft 159210 Aug 29 09:36 _output/fehmn.out

compare/fehmn.out

*********************************************************************
 Time Step        87

                    Timing Information
           Years              Days         Step Size (Days)
      25000.0000          9131250.00        0.364870000E+05
 Heat and Mass Solution Disabled
    201     0.000000E+00                 0
    201     0.000000E+00                 0
    201     0.534817E+01                 2
    201     0.267409E+01                 1


 simulation ended: days   9131250.0000000000000000     timesteps    87

_output/fehmn.out

Time Step        87

                    Timing Information
           Years              Days         Step Size (Days)
      25000.0000          9131250.00        0.364870000E+05
 Heat and Mass Solution Disabled
    201     0.000000E+00                 0
    201     0.000000E+00                 0
    201     0.534817E+01                 2
    201     0.267409E+01                 1


 simulation ended: days   9131250.0000000000000000     timesteps    87

Start by inspecting the fehmpytests comparison logic and comparing compare/fehmn.out with _output/fehmn.out for the cellbased case. Determine which stable portion should be evaluated and which differing content should be ignored; done means the cellbased fehmpytests comparison passes reliably.