Initial work on setting up tests for MultiPhysicsCrystalPlasticity that use exodiff.

Modified several CMakeLists.txt files and created run_exodiff_test.py.  So far, so
good, ctest and the python script run the correct Albany command (mpiexec, etc.), but
I still need to get exodiff itself hooked up in the cmake/python files.  Currently,
the test passes or fails based only on the return code from AlbanyT.