Improve docker build to use hooks

docker/etc/php7/php-fpm.conf

@@ -0,0 +1,19 @@
+[global]
+error_log = /proc/self/fd/2
+log_level = error
+daemonize = no
+
+[www]
+catch_workers_output = yes
+user = nginx
+group = nginx
+listen.owner = nginx
+listen.group = nginx
+listen = /var/run/php-fpm.sock
+pm = dynamic
+pm.max_children = 20
+pm.start_servers = 1
+pm.min_spare_servers = 1
+pm.max_spare_servers = 3
+pm.max_requests = 2048
+include = /etc/php7/php-fpm.d/env.conf