Fix SamplingProfiler for use in zygote

Two small fixes to fix SamplingProfilerIntegration:
- Fix name of Timer thread to match native code, allowing
    "set prop persist.sampling_profiler 1"
  to profile startup of apps.
- clone newThreads array since ThreadSet may reuse it internally
  (which is the case in SamplingProfilerIntegration's use of
   SamplingProfiler.newThreadGroupTheadSet)

Bug: 3117365
Change-Id: Ic8c2779b7961a39b87494253bb99c56e6e35ae15