A recent change tries to separate resync and relist. The motivation
was to avoid triggering relist when a resync is required.

However, the change is not effective since it stops the watcher. As hongchao
mentioned in the original comment, today's storage interface will not deliever
any progress notification to the watch chan. So any watcher that does not receive
events for the last few seconds will not be able to catch up from the previous
index after a hard close since the index of the last received event is out of
the cache window inside etcd2.

This pull request tries to fix this issue by not stoping watcher when a resync is
required.