CameraService: Don't block on camera HAL start in all cases

When initially starting up, use tryGetService instead of getService to
avoid blocking camera service start in cases where the camera HAL is stuck.

Test: atest cameraservice_test && atest CameraManagerTest, with and without
  lazy camera HAL

Change-Id: I2ad5c542e77e748902cfb49f90a55620b29ad4cd