Fix bug 15423 - server crashes when there is an outstanding read/transact on a named pipe and the client shuts down the connection.

Opening a pipe and having an outstanding async read, write or transact on it when the connection is terminated causes a server crash.

This is because we were not removing outstanding aio's on fake_file handles (which are used for pipes) in the shutdown path, as we do for files and directories.

Adds DEVELOPER only code that panics the server if we are shutting down and we have any orphaned aio requests on any handles, and then adds test code with knownfail that exercises this. Then fix and remove knownfail.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15423

Passes ci.