fix some ineffectual assignments

to make goreportcard a bit happier
https://goreportcard.com/report/github.com/docker/docker

also found that `TestCpToErrDstParentNotExists()` was
partially broken, because a `runDockerCp()` was inadvertently
removed in f26a31e80c

`TestDaemonRestartSaveContainerExitCode()` didn't verify
the actual _Error_ message, so added that to the test,
and updated the test to take into account that the
"experimental" CI enables `--init` on containers.

`TestVolumeCLICreateOptionConflict()` only checked
for an error to occur, but didn't validate if the
error was due to conflicting options.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

integration-cli/docker_cli_network_unix_test.go

@@ -497,6 +497,7 @@ func (s *DockerSuite) TestDockerInspectMultipleNetwork(c *check.C) {
 
 	networkResources = []types.NetworkResource{}
 	err = json.Unmarshal([]byte(result.Stdout()), &networkResources)
+	c.Assert(err, check.IsNil)
 	c.Assert(networkResources, checker.HasLen, 1)
 
 	// Should print an error and return an exitCode, nothing else