add support for launching tests with php interpreters

[agallou]

fixes #36

[jubianchi]

My feedback on this feature: so far, I did not run any test with docker, but:

• The configuration directive are not used:

But the plugin seems to only run /usr/bin/php ... when it should run /usr/bin/php -ddate.timzeon=UTC

• The PHP interpreter should also be given to atoum via the -p argument, something like /usr/bin/php -ddate.timzeon=UTC vendor/bin/atoum -p '/usr/bin/php -ddate.timzeon=UTC' ... : if we don't do that, atoum will always use the default php binary which ha will find in the PATH so in the case of docker, it will probably not work.

[jubianchi]

👍