lxd/instance/drivers: Handle websocket closing

When the VM disconnects due to a stop/reboot, the socket is closed and the
error we get is a `connection reset by peer` or a `Unexpected EOF` instead
of a EOF.
So this helps handle these errors similarly to make the command exit
cleanly in these scenarios.
Since both errors are of type errorString, the only way to check it
is to see if they contains the expected substring.

Signed-off-by: hamistao <pedro.ribeiro@canonical.com>

lxd/instance/drivers/driver_qemu_cmd.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"io"
 	"strconv"
+	"strings"
+	"syscall"
 
 	"golang.org/x/sys/unix"
 
@@ -80,7 +82,9 @@ func (c *qemuCmd) Wait() (int, error) {
 		// Error of type EOF indicates the session ended unexpectedly,
 		// so we inform the client of the disconnection with a more
 		// descriptive message.
-		if errors.Is(err, io.EOF) {
+		// The error can be different depending on why the VM disconnected
+		// so we handle these cases similarly.
+		if errors.Is(err, io.EOF) || strings.Contains(err.Error(), io.ErrUnexpectedEOF.Error()) || strings.Contains(err.Error(), syscall.ECONNRESET.Error()) {
 			return exitStatus, ErrExecDisconnected
 		}