Lower the problem size for test_many_domain and test_many_array

Since switching to qthreads these tests take a lot longer to execute and
test_many_domain times out pretty often. test_many_domain has also been timing
out for numa+gasnet for months

This doesn't reflect a real problem with qthreads, so much as it does a
"problem" with the testing framework. Even with qthreads configured with
oversubscription and affinity off there is still interference from multiple
qthreads instances running on the same machine.

I tested these two programs out on an xc and on a cluster, and the qthreads
version was a few seconds quicker so I'm pretty confident in my claim that it's
just how we test gasnet+qthreads that's responsible for the slow down and not
some performance mystery that needs to be explored.

These new sizes lower the execution time to ~30 seconds.