labs: restart slapd once a week
Add a cron that restarts slapd once a week to mitigate the slapd memory
leak issue, as suggested by Moritz.
Note how there are 2 other roles (corp and labtest) using the same slapd
module that are not changed so far. (Is corp not hit by the issue?)
Bug:T130593
Change-Id: Idf33099b07d3d231a0c229628db5c9d6c67dd8b0