Docker: docker_start_user.sh: make sure that grant_device_permissions doesn't...

Docker: docker_start_user.sh: make sure that grant_device_permissions doesn't exit with non-zero return code

* when docker_start_user.sh is executed from dockerfile and
  /dev/snd doesn't exist it will fail with:

  + cp -rf /opt/apollo/rcfiles/user.vimrc /home/apollo/.vimrc
  + chown -R 1001:1001 /home/apollo/. /home/apollo/.. /home/apollo/.bash_aliases /home/apollo/.bash_logout /home/apollo/.bashrc /home/apollo/.config.pycodestyle /home/apollo/.lcovrc /home/apollo/.profile /home/apollo/.vimrc
  + setup_apollo_directories 1001 1001
  + local apollo_dir=/opt/apollo
  + [[ -d /opt/apollo ]]
  + grant_device_permissions apollo
  + '[' -e /dev/novatel0 ']'
  + '[' -e /dev/novatel1 ']'
  + '[' -e /dev/novatel2 ']'
  + '[' -e /dev/ttyACM0 ']'
  + '[' -e /dev/imu ']'
  + '[' -e /dev/camera/obstacle ']'
  + '[' -e /dev/camera/trafficlights ']'
  + '[' -e /dev/snd ']'
  The command '/bin/sh -c bash -x /opt/apollo/scripts/docker_start_user.sh' returned a non-zero code: 1

scripts/docker_start_user.sh

@@ -79,6 +79,8 @@ function grant_device_permissions() {
 
   # setup audio device
   [ -e /dev/snd ] && usermod -a -G audio "$1"
+
+  true
 }
 
 function setup_apollo_directories() {