manager: fix a crash in isolating

manager: fix a crash in isolating

HASHMAP_FOREACH is safe against the removal of the current entry, but
not against the removal of other entries. job_finish_and_invalidate()
can recursively remove other entries.

It triggered an assertion failure:
  Assertion 'j->installed' failed at src/manager.c:1218, function
  transaction_apply(). Aborting.

Fix the crash by iterating from the beginning when there is a
possibility that the iterator could be invalid.

It is O(n^2) in the worst case, but that's better than a crash.

https://bugzilla.redhat.com/show_bug.cgi?id=717325