Fix race conditions closing HTTP I/O objects:
This fixes a case where stop can sometimes skip calling close on some
I/O objects or crash in a rare circumstance where a connection is in the
process of being torn down at the exact time the server is stopped. When
the acceptor receives errors, it logs the error and continues listening
instead of stopping.
Add bin/stop-test.js shutdown testing script:
This script launches rippled repeatedly and then issues a stop command
after a variable amount of time. This is to test the shutdown of the
application and catch errors.
Clear the acquiring ledger when shutting down NetworkOPs:
This solves a circular destruction problem on exit.