Make functional tests command useable with PAAS

[larowlan]

Currently the functional tests command just outputs to the console with echo

https://github.com/govCMS/scaffold-tooling/blob/8.x-develop/.gitlab-ci-main.yml#L149

This means PAAS projects can't override it without unlocking their own gitlab-ci.yml and parting ways with the scaffold template.

Provide a variable or similar or a way for the command to be overridden without forking the CI file

[acbramley]

Looks like this issue can be closed