contint: fix slave-scripts deployment on labs

We can not use git-deploy from tin.eqiad.wmnet to update instances in
labs.  CI has a bunch of slaves that needs the slave-scripts repository
to be kept up to date somehow, hence the use of git::clone in
contint::slave-scripts.

This patch:

* prevents contint::slave-scripts on production since it will conflict
  with git-deploy
* updates contint::slave-scripts clone path to match production ie:
  /srv/deployment/integration/slave-scripts
* apply contint::slave-scripts to all labs slave by including it in
  role::ci::slave::labs::common

Change-Id: I1795f325ed8afb8beb3d894ff5b0e8b89e7b085d