Restore error type in FindNetwork

The error type libnetwork.ErrNoSuchNetwork is used in the controller
to retry the network creation as a managed network though the manager.
The change of the type was breaking the logic causing the network to
not being created anymore so that no new container on that network
was able to be launched
Added unit test

Signed-off-by: Flavio Crisciani <flavio.crisciani@docker.com>
Upstream-commit: 51cea0a53c2fd36832277402e9faac81bfb4abd4
Component: engine

components/engine/integration-cli/docker_cli_netmode_test.go

@@ -49,7 +49,7 @@ func (s *DockerSuite) TestNetHostname(c *check.C) {
 	c.Assert(out, checker.Contains, "Invalid network mode: invalid container format container:<name|id>")
 
 	out, _ = dockerCmdWithFail(c, "run", "--net=weird", "busybox", "ps")
-	c.Assert(strings.ToLower(out), checker.Contains, "no such network")
+	c.Assert(strings.ToLower(out), checker.Contains, "not found")
 }
 
 func (s *DockerSuite) TestConflictContainerNetworkAndLinks(c *check.C) {