Various discretizations of 01_steady_flow test. 
Useful for scaling parallel tests.

There are two variants:

flow_bddc.con:
We prescribe continuous Dirichlet boundary condition on the surface of the cube 
given by linear function on boundary of all dimension. This problem is quite STIFF or badly conditioned. 

The transition coefficient between dimensions is constantly equal to 1.0. Therefore, the interface between dimension 
is not permeable enough to transfer flux from the 2D fractures which results to singularities in the crossection of the 2d fractures on the surface.

flow_bddc_regular.con:
We prescribe continuous Dirichlet boundary condition on the surface of the cube only for 3d elements.
2d and 1d boundaries are impermeable.