Fix hidl_ssvc_poll thread issues

1) Patch poll wake up handling logic so that thread no longer quits
   on spurious wake up.
2) Patch(simplify) thread initialization, so that it will not hang
   on waiting for conditional variable.

Test: 1) send signal 3 to system_server, does not observe thread quit.
Test: 2) adb shell "stop;start" many times, every time thread starts.

Bug: 62933449
Bug: 62933799

Merged-In: Icb7477e9d75338b9742e144fc2687d5ced91e89e
Change-Id: Icb7477e9d75338b9742e144fc2687d5ced91e89e