Add _EXTRA_PACKAGES support during build.

 FROM debian:stretch
 
+ARG NGINX_EXTRA_PACKAGES
+
 COPY files/ /tmp/files/
 RUN /tmp/files/configure
 

@@ -2,6 +2,6 @@
 
 set -e
 apt-get update
-apt-get install -y ssmtp nginx libnginx-mod-http-subs-filter
+apt-get install -y ssmtp nginx libnginx-mod-http-subs-filter $NGINX_EXTRA_PACKAGES
 rm /etc/nginx/sites-enabled/default
 cp -a /tmp/files/entrypoint.sh /sbin

 FROM node
 
+ARG NODE_EXTRA_PACKAGES
+
 COPY files/ /tmp/files/
 RUN /tmp/files/configure
 

@@ -2,7 +2,7 @@
 
 set -e
 apt-get update
-apt-get install -y ssmtp sudo
+apt-get install -y ssmtp sudo $NODE_EXTRA_PACKAGES
 #npm install -g gulp grunt
 
 cp /tmp/files/entrypoint /root/entrypoint

 FROM debian:stretch
 
+ARG PHPFPM_EXTRA_PACKAGES
+
 COPY files/ /tmp/files/
 RUN /tmp/files/configure
 

@@ -2,7 +2,7 @@
 
 set -e
 apt-get update
-apt-get install -y sudo ssmtp php7.0-fpm php7.0-mysql php7.0-imagick php7.0-ldap php7.0-xml php7.0-mbstring php7.0-mcrypt php7.0-gd php7.0-apc git ffmpeg ghostscript
+apt-get install -y sudo ssmtp php7.0-fpm php7.0-mysql php7.0-imagick php7.0-ldap php7.0-xml php7.0-mbstring php7.0-mcrypt php7.0-gd php7.0-apc $PHPFPM_EXTRA_PACKAGES
 
 rm /etc/php/7.0/fpm/pool.d/www.conf
 cp -a /tmp/files/app-defaults.conf /etc/php/7.0/fpm