adapt redis role and redis template for lab use

in redis conf templ, add param to rewrite the log when it's much
smaller, taking into account memory on labs instances
combine old labs-redis role with role::db::redis and add mem params

Change-Id: I53a0a5b1350af44f23a365d9d3f5203a576e4d48
Merge "adapt redis role and redis template for lab use" into production