Make glance nginx.sh POSIX compatible

'function' keyword is a bash extension and not recognizable by sh.

Change-Id: I96205e337a28e12f3e3d06ca99e5f04e0f9a38f4
Signed-off-by: Andrii Ostapenko <andrii.ostapenko@att.com>

glance/templates/bin/_nginx.sh.tpl

@@ -3,14 +3,14 @@ set -xe
 
 COMMAND="${@:-start}"
 
-function start () {
+start () {
   envsubst < /etc/nginx/nginx.conf > /tmp/nginx.conf
   cat /tmp/nginx.conf
   nginx -t -c /tmp/nginx.conf
   exec nginx -c /tmp/nginx.conf
 }
 
-function stop () {
+stop () {
   nginx -s stop
 }