Work around spurious epoll notifications.

Sometimes it seems like we can get into a situation where we are
unable to remove an fd from the epoll set but it keeps sending us
events anyhow.  Defensively rebuild the epoll set in this case
to prevent us from spinning forever.

Bug: 21271428
Change-Id: I5607e565f2e12460d7113a1f62a70d38d334e271