borg-backup: save PIPESTATUS before referencing

It's not obvious, but the if statements can change the PIPESTATUS
meaning we're not matching what we think we're matching.  Save the
pipestatus of the backup commands so we exit the backup script with
the right code.

Change-Id: I83c7db45d3622067eb05107e26fbdc7a8aeecf63

playbooks/roles/borg-backup/templates/borg-backup.j2

@@ -43,12 +43,13 @@ do
     bash $f | ${BORG_CREATE} --stdin-name ${stream_name} \
                       ::"{hostname}-${stream_name}-{now}" -
 
-    if [[ ${PIPESTATUS[0]} -ne 0 ]]; then
+    _status=( "${PIPESTATUS[@]}" )
+    if [[ ${_status[0]} -ne 0 ]]; then
         info "Streaming script ${f} failed!"
-        stream_exit=${PIPESTATUS[0]}
-    elif [[ ${PIPESTATUS[1]} -ne 1 ]]; then
+        stream_exit=${_status[0]}
+    elif [[ ${_status[1]} -ne 1 ]]; then
         info "Borg failed!"
-        stream_exit=${PIPESTATUS[1]}
+        stream_exit=${_status[1]}
     else
         stream_exit=0
     fi