Add testing docker container based on PHP 5.6

docker/dev/mtt-php56-apache/Dockerfile

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+
+FROM php:5.6-apache
+
+RUN docker-php-ext-install mysqli opcache && \
+	rm -f /usr/local/etc/php/conf.d/docker-php-ext-opcache.ini && \
+	mv "$PHP_INI_DIR/php.ini-production" "$PHP_INI_DIR/php.ini"

docker/dev/mtt-php56-apache/docker-compose.yml

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+version: '3'
+services:
+  web:
+    build: ./
+    image: mtt-php5.6-apache
+    container_name: mtt-php56-apache
+    ports:
+    - "8080:80"
+    volumes:
+    - ../../../src:/var/www/html
+    - ./php-mtt.ini:/usr/local/etc/php/conf.d/php-mtt.ini
+    - ./php-opcache.ini:/usr/local/etc/php/conf.d/php-opcache.ini

docker/dev/mtt-php56-apache/php-mtt.ini

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+
+; Since PHP 5.4 E_STRICT is included in E_ALL
+error_reporting = E_ALL
+
+log_errors = On
+display_errors = On
+display_startup_errors = On

docker/dev/mtt-php56-apache/php-opcache.ini

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+;; opcache.ini
+
+;; check /usr/local/etc/php/conf.d if exists docker-php-ext-opcache.ini
+
+; To disable opcache just comment this line
+zend_extension=opcache.so
+
+[opcache]
+opcache.enable=0
+opcache.enable_cli=0
+
+; The size of the shared memory storage used by OPcache, in megabytes. The minimum permissible value is "8", which is enforced if a smaller value is set.
+; Default is 128.
+opcache.memory_consumption=128
+
+; The maximum number of keys (and therefore scripts) in the OPcache hash table.
+; The actual value used will be the first number in the set of prime numbers
+;  { 223, 463, 983, 1979, 3907, 7963, 16229, 32531, 65407, 130987, 262237, 524521, 1048793 }
+;  that is greater than or equal to the configured value.
+; The minimum value is 200. The maximum value is 1000000. Values outside of this range are clamped to the permissible range.
+; Default is 10000.
+opcache.max_accelerated_files=1000
+
+; How often to check script timestamps for updates, in seconds. 0 will result in OPcache checking for updates on every request.
+; This configuration directive is ignored if opcache.validate_timestamps is disabled.
+; Default is 2.
+opcache.revalidate_freq=2
+
+; If enabled, OPcache will check for updated scripts every opcache.revalidate_freq seconds.
+; When this directive is disabled, you must reset OPcache manually via opcache_reset(), opcache_invalidate()
+;  or by restarting the Web server for changes to the filesystem to take effect.
+; Default is 1.
+;; Override in docker-compose
+opcache.validate_timestamps=1