This always slept for 3 seconds, waiting for the storage to
disconnect.  This loses on two counts:

1. Since the timeout is set to 1 second, it typically sleeps
   longer than necessary.

2. Since there's no predicting thread and process scheduling,
   3 seconds isn't always long enough, and rare failures have
   been reported against this test.

Instead we do a polling loop now.  This typically succeeds in
a little more than a second, speeding the normal case.  The
loop will continue trying for up to a minute if not.