allow very long timeouts for asynchronous tests
allow very long timeouts for asynchronous tests

- rare test invocations managed to outlast the 1-second timeout
  when run on virtual machines with few cores.
  (observed once in thousands of test runs)
- if a test manages to outlast the 10-second timeout,
  that should indicate a bug.

glessard/swift-atomics,glessard/swift-atomics,glessard/swift-atomics