lxd-agent: Log start time mount args on error

Signed-off-by: Thomas Parrott <thomas.parrott@canonical.com>

lxd-agent/main_agent.go

@@ -324,7 +324,7 @@ func (c *cmdAgent) mountHostShares() {
 
 		_, err = shared.RunCommand("mount", args...)
 		if err != nil {
-			l.Error("Failed to mount", logger.Ctx{"err": err})
+			l.Error("Failed to mount", logger.Ctx{"err": err, "args": args})
 			continue
 		}