Add some test_num_threads for guvectorize
Add some test_num_threads for guvectorize

Note that some of these tests don't actually work yet

- The test of calling set_num_threads inside of a guvectorized function does
  not work in workqueue

- The test to check how many threads are used by reading get_thread_num() does
  not work, presumably because the function is only called once. I'm unsure
  how to test this properly.

IntelLabs/numba,stonebig/numba,stonebig/numba,numba/numba,stuartarchibald/numba,sklam/numba,numba/numba,cpcloud/numba,numba/numba,gmarkall/numba,stuartarchibald/numba,sklam/numba,IntelLabs/numba,stuartarchibald/numba,seibert/numba,cpcloud/numba,sklam/numba,gmarkall/numba,seibert/numba,sklam/numba,gmarkall/numba,IntelLabs/numba,cpcloud/numba,gmarkall/numba,cpcloud/numba,stonebig/numba,seibert/numba,stuartarchibald/numba,seibert/numba,stonebig/numba,IntelLabs/numba,stonebig/numba,seibert/numba,cpcloud/numba,numba/numba,stuartarchibald/numba,IntelLabs/numba,numba/numba,gmarkall/numba,sklam/numba