Add Behat tests

Added some behat test covering pickle. Four suites have been created:

* Pickle source (`pickle`)
* Pickle Phar (`pickle_phar`)
* PECL extensions conversion with Pickle source (`pecl`)
* PECL extensions conversion with Pickle Phar (`phar_pecl`)
this line is specific to the needs of Behat (Pickle will not even run on HHVM as it does not make sense)