wrong if root check at extend_start

Some images have a check to clean and source apache environment variables when the user is root.
However this check is not evaluating properly:

if [[ $USER == "root" ]]; then
    echo "root" > /tmp/user
else
    echo "nonroot" > /tmp/user
    whoami >> /tmp/user
fi

In ubuntu causes this output not evaluating correctly the first condition

docker exec cinder_api cat /tmp/user
nonroot
root

This is fixed changing to if [[ $EUID -eq 0 ]]

Error while launched cinder-api under apache:

Running command: '/usr/sbin/apache2 -DFOREGROUND'
[Fri May 12 12:13:13.958660 2017] [core:warn] [pid 6] AH00111: Config variable ${APACHE_LOCK_DIR} is not defined
[Fri May 12 12:13:13.958720 2017] [core:warn] [pid 6] AH00111: Config variable ${APACHE_PID_FILE} is not defined
[Fri May 12 12:13:13.958731 2017] [core:warn] [pid 6] AH00111: Config variable ${APACHE_RUN_USER} is not defined
[Fri May 12 12:13:13.958736 2017] [core:warn] [pid 6] AH00111: Config variable ${APACHE_RUN_GROUP} is not defined
[Fri May 12 12:13:13.958744 2017] [core:warn] [pid 6] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Fri May 12 12:13:13.961974 2017] [core:warn] [pid 6:tid 139992602384256] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Fri May 12 12:13:13.962176 2017] [core:warn] [pid 6:tid 139992602384256] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Fri May 12 12:13:13.962193 2017] [core:warn] [pid 6:tid 139992602384256] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
AH00526: Syntax error on line 74 of /etc/apache2/apache2.conf:
Invalid Mutex directory in argument file:${APACHE_LOCK_DIR}