Work on consistent/safe way to use PetscOptions and/or file options in tests

[cekees]

The PetscOptions data base is global and persistent, so our unit tests can be effected by the order in which tests are run. We need to clear and fully specify the options for each tests to make them atomistic.

[cekees]

• closes p1 and p2 linear solver options used in petsc.options not converging for SIPG #14
• closes c0p2 not converging with petsc conjugate gradients (cg) #15