Preserve HTTP worker state after exception

threadedhttp.Http.request set self.follow_redirects=False before calling its
parent method, and reset it afterwards.  However if there was an exception
in the parent method, self.follow_redirects was not reset and changed
the behaviour of subsequent requests handled by the HTTP worker.

Change-Id: I1b917fbcea4ad51a958ec19faea4f2618662f6a8
Merge "Preserve HTTP worker state after exception"