Fix flapping "scrub" test

tests/test_scrub.sh

@@ -20,6 +20,9 @@ LD_PRELOAD="build/src/libfio_vitastor.so" \
     fio -thread -name=test -ioengine=build/src/libfio_vitastor.so -bs=1M -direct=1 -iodepth=4 \
         -mirror_file=./testdata/mirror.bin -end_fsync=1 -rw=write -etcd=$ETCD_URL -image=testimg
 
+# Save PG primary
+primary=$($ETCDCTL get --print-value-only /vitastor/config/pgs | jq -r '.items["1"]["1"].primary')
+
 # Intentionally corrupt OSD data and restart it
 zero_osd_pid=OSD${ZERO_OSD}_PID
 kill ${!zero_osd_pid}
@@ -34,6 +37,9 @@ start_osd $ZERO_OSD
 # Wait until start
 wait_up 10
 
+# Wait until PG is back on the same primary
+wait_condition 10 "$ETCDCTL"$' get --print-value-only /vitastor/config/pgs | jq -s -e \'.[0].items["1"]["1"].primary == "'$primary'"'"'"
+
 # Trigger scrub
 $ETCDCTL put /vitastor/pg/history/1/1 `$ETCDCTL get --print-value-only /vitastor/pg/history/1/1 | jq -s -c '(.[0] // {}) + {"next_scrub":1}'`