[T] Replace static var in tests with an outer def.

Running this test multiple times using
--gtest_repeat caused an error because of the
static modifier.

I would suggest not to use static in tests,
because the state of the test depends on execution
order.
Merge pull request #437 from endJunction/CorrectTestTimeStepping

[T] Replace static var in tests with an outer def.
Shuffle and repeat tests 3 times on Travis.
Disable MPI tests when shuffling.
Merge pull request #438 from bilke/travis-shuffle-repeat

Shuffle and repeat tests on Travis