worker_start: allow ARCHIVE variable override
The worker_start.sh script is using archive directory inside
the worker user home which cannot be changed, this patches
allows override ARCHIVE environment variable to address
this issue.
# A simple script used by Red Hat to start teuthology-worker processes.
-ARCHIVE=$HOME/archive
+ARCHIVE=${ARCHIVE:-"$HOME/archive"}
WORKER_LOGS=$ARCHIVE/worker_logs
function start_workers_for_tube {
