Detect more kinds of s3fs mount failures

s3fs can claim to have a mount even though it didn't succeed.
Doing an operation actually forces it to detect that and remove the mount.
+ls "${AWS_S3_MOUNT}"

docker-entrypoint.sh

@@ -69,6 +69,10 @@ su - $RUN_AS -c "s3fs $DEBUG_OPTS ${S3FS_ARGS} \
     -o gid=$GID \
     ${AWS_S3_BUCKET} ${AWS_S3_MOUNT}"
 
+# s3fs can claim to have a mount even though it didn't succeed.
+# Doing an operation actually forces it to detect that and remove the mount.
+ls "${AWS_S3_MOUNT}"
+
 mounted=$(mount | grep fuse.s3fs | grep "${AWS_S3_MOUNT}")
 if [ -n "${mounted}" ]; then
     echo "Mounted bucket ${AWS_S3_BUCKET} onto ${AWS_S3_MOUNT}"