Fix not found being raised when iterating

Instead of re-raising a not found exception just
silence those exceptions when iterating (and do not
yield that job back in the first place) and then
remove the job from the jobboard internals to avoid
further iteration.

Fixes bug 1304562

Change-Id: Ibc6d3ea55dc19e70104bfc801283b8ad919496c4
Merge "Fix not found being raised when iterating"