[docker] Install memcached PHP extension from PECL (#1473)

- Adapted from https://stackoverflow.com/a/41575677
- Tested by running `php -m`
- SimpleXML now comes pre-installed with PHP, so removed the extra step
- Adds --no-install-recommends

Signed-off-by: Nemo <me@captnemo.in>

Dockerfile

@@ -3,20 +3,15 @@ FROM php:7-apache
 ENV APACHE_DOCUMENT_ROOT=/app
 
 RUN mv "$PHP_INI_DIR/php.ini-production" "$PHP_INI_DIR/php.ini" \
-	&& apt-get --yes update && apt-get --yes install libxml2-dev zlib1g-dev libmemcached-dev \
-	&& docker-php-ext-install -j$(nproc) simplexml \
+	&& apt-get --yes update \
+	&& apt-get --yes --no-install-recommends install \
+		zlib1g-dev \
+		libmemcached-dev \
+	&& pecl install memcached \
+	&& docker-php-ext-enable memcached \
 	&& sed -ri -e 's!/var/www/html!${APACHE_DOCUMENT_ROOT}!g' /etc/apache2/sites-available/*.conf \
 	&& sed -ri -e 's!/var/www/!${APACHE_DOCUMENT_ROOT}!g' /etc/apache2/apache2.conf /etc/apache2/conf-available/*.conf \
 	&& sed -ri -e 's/(MinProtocol\s*=\s*)TLSv1\.2/\1None/' /etc/ssl/openssl.cnf \
 	&& sed -ri -e 's/(CipherString\s*=\s*DEFAULT)@SECLEVEL=2/\1/' /etc/ssl/openssl.cnf
 
-RUN curl https://codeload.github.com/php-memcached-dev/php-memcached/tar.gz/v3.1.5 --output /tmp/php-memcached.tar.gz \
-	&& mkdir -p /usr/src/php/ext \
-	&& tar xzvf /tmp/php-memcached.tar.gz -C /usr/src/php/ext \
-	&& mv /usr/src/php/ext/php-memcached-3.1.5 /usr/src/php/ext/memcached \
-	&& cd /usr/src/php/ext/memcached \
-	&& docker-php-ext-configure /usr/src/php/ext/memcached --disable-memcached-sasl \
-	&& docker-php-ext-install /usr/src/php/ext/memcached \
-	&& rm -rf /usr/src/php/ext/memcached
-
 COPY --chown=www-data:www-data ./ /app/