Add support for php.ini variables containing special chars

[nguyenk]

My php container that connects to redis (with password)

api:
    image: thecodingmachine/php:7.1-v1-apache
    ...
    environment:
      ...
      PHP_INI_SESSION__SAVE_HANDLER: redis
      PHP_INI_SESSION__SAVE_PATH: "tcp://redis:6379?auth=123"

When I try to access redis session store, I get the following error :
session_start(): open(tcp://redis:6379?auth/sess_p6rqfk7phj43d477k37d3iecb4, O_RDWR) failed: No such file or directory

It seems that the the variable has been stripped after the equal sign.