Add test environment for PHP 5.6 and PHP 7.0

[Shelob9]

Resolves #3431 by adding and documenting two new test sites in the local test environment

[New0]

@Shelob9 the change here works but I think we didn't update composer commands to run yarn instead of npm in that case and would need to adapt nuke and dev:install commands, isn't it?

[Shelob9]

@New0 Yes, need updated to use yarn, not npm

[New0]

@Shelob9 That is working for me but I wanted to know if there is a way to run PHP Unit tests selecting the environment?