Fix status report when key generation is inflight

This is a pain to test because it fails only when we are actively generating keys.

@oferrigni @marcparadise @sdelano @tylercloke @doubt72 @jmink
I'd almost rather see this handled in the status function, so that it returns either a separate field or replaces the value itself.  This way chef_wm_status doesn't need to have knowledge of chef_keygen internals.