POC: Introduce Nextcloud based on Nginx web server.

This PR introduce POC of Nextcloud based on Nginx web server with php-fpm in separated container.
Basic installation with SQLite and few operations in web gui were tested.

Nginx dockerfile is generated from Dockerfile-nginx.template
  - FROM string has hardcoded variant - apache
  - There is no upstream PHP image with Nginx, due this generate-stackbrew-library is not able to identify parent correctly

New files were introduced in image:
  - Dockerfile-nginx.template
  - nginx-foreground
    + simulates behavior of apache2-foreground cmd
  - 16.0/nginx/Dockerfile
    + generated from template Dockerfile-nginx.template
  - nextcloud.confx
    + Nginx vhost configuration
  - start_net.sh (temporary)
    + Helper script to create user-defined network for Docker
    + '--link' option for docker create is obsolete and we need communication between fpm and nginx container
  - start_container.sh (temporary)
    + Helper script to handle containers
  - Dockerfile
    + /Dockerfile for verification purposes
Updated files:
  - set -x added to all shell scripts for easier troubleshooting (temporary)
  - update.sh
    + New variant introduced
    + Number of builded variant is limited for simplified CI.
  - .travis.yml (temporary)
    + Image push to registry for testing purposes
  - docker-entrypoint.sh
    + Recognizes new argument for entrypoint - nginx-foreground

Be careful during review, github recognizes removed files for 15.0 release as renamed to 16.0/nginx variant

Motivation/Usecase:
  - I have openvz based VPS where only old Docker 1.10 is supported.
  - Apache(in nextcloud container) in combination Nginx as a reverse proxy for multiple vhosts doesn't work correctly

Image pull link:
docker pull 1john2ci/nextcloud:apache-20190509
docker pull 1john2ci/nextcloud:fpm-20190509
Travis CI test: 530329740

Deployment notes:
  - Clone source code
  - Create user-defined network for Docker
  - Start fpm container
  - Start nginx container

16.0/nginx/config/apcu.config.php

@@ -0,0 +1,4 @@
+<?php
+$CONFIG = array (
+  'memcache.local' => '\OC\Memcache\APCu',
+);

16.0/nginx/config/apps.config.php

@@ -0,0 +1,15 @@
+<?php
+$CONFIG = array (
+  "apps_paths" => array (
+      0 => array (
+              "path"     => OC::$SERVERROOT."/apps",
+              "url"      => "/apps",
+              "writable" => false,
+      ),
+      1 => array (
+              "path"     => OC::$SERVERROOT."/custom_apps",
+              "url"      => "/custom_apps",
+              "writable" => true,
+      ),
+  ),
+);

16.0/nginx/config/autoconfig.php

@@ -0,0 +1,29 @@
+<?php
+
+$autoconfig_enabled = false;
+
+if (getenv('SQLITE_DATABASE')) {
+    $AUTOCONFIG["dbtype"] = "sqlite";
+    $AUTOCONFIG["dbname"] = getenv('SQLITE_DATABASE');
+    $autoconfig_enabled = true;
+} elseif (getenv('MYSQL_DATABASE') && getenv('MYSQL_USER') && getenv('MYSQL_PASSWORD') && getenv('MYSQL_HOST')) {
+    $AUTOCONFIG["dbtype"] = "mysql";
+    $AUTOCONFIG["dbname"] = getenv('MYSQL_DATABASE');
+    $AUTOCONFIG["dbuser"] = getenv('MYSQL_USER');
+    $AUTOCONFIG["dbpass"] = getenv('MYSQL_PASSWORD');
+    $AUTOCONFIG["dbhost"] = getenv('MYSQL_HOST');
+    $autoconfig_enabled = true;
+} elseif (getenv('POSTGRES_DB') && getenv('POSTGRES_USER') && getenv('POSTGRES_PASSWORD') && getenv('POSTGRES_HOST')) {
+    $AUTOCONFIG["dbtype"] = "pgsql";
+    $AUTOCONFIG["dbname"] = getenv('POSTGRES_DB');
+    $AUTOCONFIG["dbuser"] = getenv('POSTGRES_USER');
+    $AUTOCONFIG["dbpass"] = getenv('POSTGRES_PASSWORD');
+    $AUTOCONFIG["dbhost"] = getenv('POSTGRES_HOST');
+    $autoconfig_enabled = true;
+}
+
+if ($autoconfig_enabled) {
+    $AUTOCONFIG["dbtableprefix"] = getenv('NEXTCLOUD_TABLE_PREFIX') ?: "";
+
+    $AUTOCONFIG["directory"] = getenv('NEXTCLOUD_DATA_DIR') ?: "/var/www/html/data";
+}

16.0/nginx/config/redis.config.php

@@ -0,0 +1,12 @@
+<?php
+if (getenv('REDIS_HOST')) {
+  $CONFIG = array (
+    'memcache.distributed' => '\OC\Memcache\Redis',
+    'memcache.locking' => '\OC\Memcache\Redis',
+    'redis' => array(
+      'host' => getenv('REDIS_HOST'),
+      'port' => getenv('REDIS_HOST_PORT') ?: 6379,
+    ),
+  );
+}
+

16.0/nginx/config/smtp.config.php

@@ -0,0 +1,15 @@
+<?php
+if (getenv('SMTP_HOST') && getenv('MAIL_FROM_ADDRESS') && getenv('MAIL_DOMAIN')) {
+  $CONFIG = array (
+    'mail_smtpmode' => 'smtp',
+    'mail_smtphost' => getenv('SMTP_HOST'),
+    'mail_smtpport' => getenv('SMTP_PORT') ?: (getenv('SMTP_SECURE') ? 465 : 25),
+    'mail_smtpsecure' => getenv('SMTP_SECURE') ?: '',
+    'mail_smtpauth' => getenv('SMTP_NAME') && getenv('SMTP_PASSWORD'),
+    'mail_smtpauthtype' => getenv('SMTP_AUTHTYPE') ?: 'LOGIN',
+    'mail_smtpname' => getenv('SMTP_NAME') ?: '',
+    'mail_smtppassword' => getenv('SMTP_PASSWORD') ?: '',
+    'mail_from_address' => getenv('MAIL_FROM_ADDRESS'),
+    'mail_domain' => getenv('MAIL_DOMAIN'),
+  );
+}