Bug#26595288 5.7 STARTUP SCRIPTS ALWAYS INITIALIZE IF EMPTY DATADIR

Add option to skip automatic init, making it possible to opt-out.
Default is still to perform init.

To skip init, create file /etc/sysconfig/mysql with contents like:

NO_INIT=true

Author: trosten

scripts/systemd/mysqld_pre_systemd.in

@@ -41,6 +41,10 @@ install_validate_password_sql_file () {
 install_db () {
     # Note: something different than datadir=/var/lib/mysql requires SELinux policy changes (in enforcing mode)
 
+    # No automatic init wanted
+    [ -e /etc/sysconfig/mysql ] && . /etc/sysconfig/mysql
+    [ -n "$NO_INIT" ] && exit 0
+
     local instance=$1
     datadir=$(get_option mysqld datadir "/var/lib/mysql${instance:+-$instance}" $instance)
     log=$(get_option mysqld 'log[_-]error' "/var/log/mysql${instance:+-$instance}.log" $instance)