open("/dev/rtc0") failure in AlarmManagerService.setTime() should be non-fatal

Setting the time-of-day clock is still useful on systems where the RTC
device is not yet brought up or otherwise unavailable.  This matches the
in-kernel behavior of the Android alarm driver.

Change-Id: I6d4fdadab12e241ada7419425efd55bd13873c55
Signed-off-by: Greg Hackmann <ghackmann@google.com>