labs: fix wbatch autostart_reset

The seemingly plausible construct used to chain two conditional commands
together doesn't work. The second command in the chain is executed
unconditionally.

The construct is replaced by a solution that lacks elegance but makes up
for it by working as intended.

Change-Id: I0bc60fdc061a51205cbbf101f6c5b16f85342afa
Implements: blueprint openstack-training-labs
Merge "labs: fix wbatch autostart_reset"