CentOS 7: increase number of open files

there's per package limitation of 100 web sites. So, vesta should limit
number of sites anyway. However, if one would want to have, for example,
350 web sites, he will be limited by OS settings.

so, lets remove limitation on the OS level and let vesta control things

install/vst-install-rhel.sh

@@ -851,6 +851,11 @@ if [ "$nginx" = 'yes' ]; then
     wget $vestacp/logrotate/nginx -O /etc/logrotate.d/nginx
     echo > /etc/nginx/conf.d/vesta.conf
     mkdir -p /var/log/nginx/domains
+    if [ "$release" -eq 7 ]; then
+        mkdir /etc/systemd/system/nginx.service.d/
+        echo "[Service]" > /etc/systemd/system/nginx.service.d/limits.conf
+        echo "LimitNOFILE=500000" >> /etc/systemd/system/nginx.service.d/limits.conf
+    fi
     chkconfig nginx on
     service nginx start
     check_result $? "nginx start failed"
@@ -889,6 +894,11 @@ if [ "$apache" = 'yes'  ]; then
     chmod a+x /var/log/httpd
     mkdir -p /var/log/httpd/domains
     chmod 751 /var/log/httpd/domains
+    if [ "$release" -eq 7 ]; then
+        mkdir /etc/systemd/system/httpd.service.d/
+        echo "[Service]" > /etc/systemd/system/httpd.service.d/limits.conf
+        echo "LimitNOFILE=500000" >> /etc/systemd/system/httpd.service.d/limits.conf
+    fi
     chkconfig httpd on
     service httpd start
     check_result $? "httpd start failed"