client: UUIDIterator: Make sure marked_as_failed status is always reset to...

client: UUIDIterator: Make sure marked_as_failed status is always reset to false, even in case of concurrent threads. (Fixes bug "Assertion `!(*current_uuid_)->marked_as_failed' failed.")

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@2730 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534