role/labs: touch an empty conf file in sites-local

"Include sites-local/*" will fail if the directory is empty, and the
IncludeOptional directive is only available on Apache 2.3.6 and later.

Change-Id: Ic41f3d85ed9eb21d6676a85b5abc40cb8a804254
Merge "role/labs: touch an empty conf file in sites-local" into production