lxc/exec: Use operation to wait directly.

When a user calls `lxc exec` the CLI calls ExecInstance, which in turn
attempts to set up an event listener to be used when interacting with
the resulting operation. However, this fails in the case where a user
does not have permission to view events in the project. Instead, we can
use the returned operation ID to wait for it to complete directly via
the API.

Signed-off-by: Mark Laing <mark.laing@canonical.com>

lxc/exec.go

@@ -202,10 +202,14 @@ func (c *cmdExec) Run(cmd *cobra.Command, args []string) error {
 	}
 
 	// Wait for the operation to complete
-	err = op.Wait()
-	opAPI := op.Get()
-	if opAPI.Metadata != nil {
-		exitStatusRaw, ok := opAPI.Metadata["return"].(float64)
+	currentOp := op.Get()
+	finishedOp, _, err := d.GetOperationWait(currentOp.ID, -1)
+	if err != nil {
+		return err
+	}
+
+	if finishedOp.Metadata != nil {
+		exitStatusRaw, ok := finishedOp.Metadata["return"].(float64)
 		if ok {
 			c.global.ret = int(exitStatusRaw)
 		}