Add sync to script that writes the RPi SD card.

Change-Id: Ia7b3709ed6a70b4e7cca521818cb59d4851f5370
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/433003
Reviewed-by: Kevin Lubick <kjlubick@google.com>
diff --git a/skolo/raspberry-pi/switchboard/configure-image-impl.sh b/skolo/raspberry-pi/switchboard/configure-image-impl.sh
index b4c4ea6..18c3de9 100755
--- a/skolo/raspberry-pi/switchboard/configure-image-impl.sh
+++ b/skolo/raspberry-pi/switchboard/configure-image-impl.sh
@@ -15,4 +15,4 @@
 
 echo ${HOSTNAME} > ${MOUNT}/etc/hostname
 install -D --mode=600 ${REL}/../../authorized_keys ${MOUNT}/root/.ssh/authorized_keys
-
+sync --file-system ${MOUNT}/root/.ssh/authorized_keys