Add ASSERT into value_list implementations.

- Field*<...>::value_list implementations check that elements of
  result vector (value_list) has correct number of rows. This is
  necessary for variable size vectors.

- Add slow default implementation into FieldAlgorithmBase and use it
  in FieldInterpolatedP0

- use only python2.7

- use python suppression file unit tests
Fix field_speed_test

- set correct shape of values in value_list