unit: count deserialized job only after it's definitely installed

Installation of a deserialized job may fail (though purely in theory),
so increase the running job counter only when succeeding.
manager: turn a superfluous check into assert

The crash that the check prevented has been fixed by commit 9e9e2b7.
job: print the "OK" status messages in normal green

The "OK" status messages should not draw attention to themselves.
It's better if they're not printed in bright/bold. Leave that
to errors and warnings.

Use a plain inconspicuous enterprisey green.