Allow PHP Variable changes for alpine images

[juanmrad]

Same changes done on pr #7 but for alpine entrypoint.

[juanmrad]

@Chekote please don't forget this. I do have a question since apparently this alpine image has the following config files:

drwxr-xr-x    4 root     root          4096 Aug  5 19:19 .
drwxr-xr-x    1 root     root          4096 Aug  5 19:28 ..
drwxr-xr-x    2 root     root          4096 Aug  5 19:19 conf.d
drwxr-xr-x    2 root     root          4096 Aug  5 19:19 fpm.d
-rw-r--r--    1 root     root         22981 Aug  5 19:19 php-fpm.conf
-rw-r--r--    1 root     root         73884 Aug  5 19:19 php.ini

There is no CLI version.

also tested by running:

$ docker build -f alpine/php5.docker . 
Successfully built f4618e4a94f4
$ docker run -e PHP_ALL_SESSION__SAVE_HANDLER=redis f4618e4a94f4 php -i | grep session.save_handler
session.save_handler => redis => redis

[Chekote]

I feel like since the current setup for the Alpine images is not supporting a distinction between CLI and FPM, we should not pretend to support those in the Image. We should either only support PHP_ALL_ variables, or modify the Alpine image to make have a separate config for CLI and FPM.