ServerService and ServerShutdownHandler are not embedded-friendly

ServerService and ServerShutdownHandler are both unfriendly to embedding as they call System.exit (in the case of ServerService only in the case of critical boot failures.)

Simplest fix is to use SystemExiter and have the embedded server code swap in an approproite Exiter. Only thing I don't like about that is SystemExiter is base on static fields and seems to have been written for testing.