Bugfix/no skip

Separates test suite into tests that can run from a single process with `nosetests` (or `python -m unittest discover`) and tests that need to be run in parallel with MPI, via `mpiexec -n <np> nosetests`.  Adds make targets to setup and teardown an ipcluster suitable for testing, and a `test` target for running all tests.

These changes clean things up somewhat and make it so that the client-side tests don't skip when being run under mpiexec, and vice versa.  We no longer get "OK ran 47 tests, 28 skipped," just "OK, ran 19 tests."

Test files that must be run in parallel via mpiexec should be named "paralleltest_<name>.py"; there is a pattern to select these files and run them appropriately; again, see the Makefile.