1-d Z Cartesian regridding fix and test

[davidhassell]

Bug fix for #715

Discovered when this tutorial example code failed with ValueError: Z coordinate 'dimensioncoordinate0' must match exactly an element of 'axes' (['domainaxis0'])

    >>> v = cf.read('vertical.nc')[0]
   >>> print(v)
   Field: eastward_wind (ncvar%ua)
   -------------------------------
   Data            : eastward_wind(time(3), air_pressure(5), grid_latitude(11), grid_longitude(10)) m s-1
   Cell methods    : time(3): mean
   Dimension coords: time(3) = [1979-05-01 12:00:00, 1979-05-02 12:00:00, 1979-05-03 12:00:00] gregorian
                   : air_pressure(5) = [850.0, ..., 50.0] hPa
                   : grid_latitude(11) = [23.32, ..., 18.92] degrees
                   : grid_longitude(10) = [-20.54, ..., -16.58] degrees
   Auxiliary coords: latitude(grid_latitude(11), grid_longitude(10)) = [[67.12, ..., 66.07]] degrees_north
                   : longitude(grid_latitude(11), grid_longitude(10)) = [[-45.98, ..., -31.73]] degrees_east
   Coord references: grid_mapping_name:rotated_latitude_longitude
   >>> new_z = cf.DimensionCoordinate(data=cf.Data([800, 705, 632, 510, 320.], 'hPa'))
   >>> new_v = v.regridc([new_z], axes='Z', method='linear', z='Z', ln_z=True)
   >>> print(new_v)
   Field: eastward_wind (ncvar%ua)
   -------------------------------
   Data            : eastward_wind(time(3), Z(5), grid_latitude(11), grid_longitude(10)) m s-1
   Cell methods    : time(3): mean
   Dimension coords: time(3) = [1979-05-01 12:00:00, 1979-05-02 12:00:00, 1979-05-03 12:00:00] gregorian
                   : Z(5) = [800.0, ..., 320.0] hPa
                   : grid_latitude(11) = [23.32, ..., 18.92] degrees
                   : grid_longitude(10) = [-20.54, ..., -16.58] degrees
   Auxiliary coords: latitude(grid_latitude(11), grid_longitude(10)) = [[67.12, ..., 66.07]] degrees_north
                   : longitude(grid_latitude(11), grid_longitude(10)) = [[-45.98, ..., -31.73]] degrees_east
   Coord references: grid_mapping_name:rotated_latitude_longitude

[sadielbartholomew]

I have confirmed that this isolates the bug with a test and fixes it in a logical way. We should probably add a Changelog entry so we don't lose track of the fix, so ideally add one now here, but otherwise this is all good, so please merge.

[davidhassell]

No need for a new change log entrry, as the existing

* Added 3-d spherical regridding to `cf.Field.regrids`, and the option
  to regrid the vertical axis in logarithmic coordinates to
  `cf.Field.regrids` and `cf.Field.regridc`
  (https://github.com/NCAS-CMS/cf-python/issues/715)

covers it - this PR is raised against that issue.

[sadielbartholomew]

Oh fair, good point. Thanks David.