Add atomic tests that use the returned value

[adayton1]

RAJA atomic operations not only perform an update but also return the value observed before the update. Our testing only appears to check that the atomic updates are correct. We are missing tests that check that the returned values are correct (or at least sensical).

For example, with an atomic increment we could check that all the values between 0 and a certain number are returned with no duplicates.

[MrBurmark]

Given the way that we use things like atomic increment to add things to arrays, I think that's definitely a hole in our coverage.