Add fpm-alpine variant (redux)

[tianon]

Closes#129 (changes reflected here)

Here's the full diff following this PR:

diff --git a/Dockerfile-debian.template b/Dockerfile-alpine.template
index 2b39553..0bda827 100644
--- a/Dockerfile-debian.template+++ b/Dockerfile-alpine.template@@ -1,18 +1,30 @@
FROM php:%%PHP_VERSION%%-%%VARIANT%%
+# our docker-entrypoint.sh is a bit involved+RUN apk add --no-cache bash+# in theory, it is POSIX-compliant, but first priority is a working, consistent image+
# install the PHP extensions we need
RUN set -ex; \
\
- apt-get update; \- apt-get install -y \- libjpeg-dev \- libpng12-dev \+ apk add --no-cache --virtual .build-deps \+ libjpeg-turbo-dev \+ libpng-dev \
; \
- rm -rf /var/lib/apt/lists/*; \
\
docker-php-ext-configure gd --with-png-dir=/usr --with-jpeg-dir=/usr; \
- docker-php-ext-install gd mysqli opcache-# TODO consider removing the *-dev deps and only keeping the necessary lib* packages+ docker-php-ext-install gd mysqli opcache; \+ \+ runDeps="$( \+ scanelf --needed --nobanner --recursive \+ /usr/local/lib/php/extensions \+ | awk '{ gsub(/,/, "\nso:", $2); print "so:" $2 }' \+ | sort -u \+ | xargs -r apk info --installed \+ | sort -u \+ )"; \+ apk add --virtual .wordpress-phpexts-rundeps $runDeps; \+ apk del .build-deps
# set recommended PHP.ini settings
# see https://secure.php.net/manual/en/opcache.installation.php

[tianon]

Simple size comparison:

wordpress fpm 1f589e64cf03 4 minutes ago 401.7 MB
wordpress fpm-alpine 174e2e2d15ff 14 minutes ago 95.41 MB

[tianon]

IMO we should review and merge docker-library/official-images#2436 before we do this one (and obviously then restart Travis here so these new variants get tested)

[tianon]

The test from docker-library/official-images#2436 caught an issue where BusyBox sed can't seem to handle some of our sed expressions, so our configuration was not being applied correctly! 👍

[tianon]

📗