rbf100{1,2}: set vm.overcommit_memory = 1, per redis requirements

Fixes:

    # WARNING overcommit_memory is set to 0! Background
    save may fail under low memory condition. To fix this issue add
    'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the
    command 'sysctl vm.overcommit_memory=1' for this to take effect.

Change-Id: I40f8675d8f352719afc234551a32334db72770ef
If persistence is neither "both" nor "rdb", disable rdb snapshots in redis

Change-Id: I71a9a89ff71b69bb6e528356050b999c204ddbad
Merge "rbf100{1,2}: set vm.overcommit_memory = 1, per redis requirements" into production