TQ: don't claim tasks panicked when they haven't

[hawkw]

tokio::task::JoinSet::join_next_with_id can return a JoinError if a task has panicked or if a task sapwned on the JoinSet was aborted through its AbortHandle...which the trust-quorum ConnectionManager will do when disconnecting a client connection:

omicron/trust-quorum/src/connection_manager.rs

Lines 866 to 886 in e00aaba

	if let Some(handle) = self.connecting.remove2(&addr) {
	// The connection has not yet completed its handshake
	info!(
	self.log,
	"Deleting initiating connection";
	"remote_addr" => %addr
	);
	handle.abort();
	None
	} else if let Some(handle) = self.established.remove3(&addr) {
	info!(
	self.log,
	"Deleting established connection";
	"peer_addr" => %addr,
	"peer_id" => %handle.baseboard_id
	);
	handle.abort();
	Some(handle)
	} else {
	None
	}

This is a normal operation and probably deserves to be logged at a less verbose level than Warn, and the log line which suggests both cancelled and panicked JoinErrors are panics is incorrect. This is a potential red herring while debugging, so I've changed it to be more accurate.