integration: copy loop variable into parallel test closures

Discovered a few instances, where loop variable is incorrectly used
within a test closure, which is marked as parallel.
Few of these were actually loops over singleton slices, therefore the issue
might not have surfaced there (yet), but it is good to fix there as
well, as this is an incorrect pattern used across different tests.

Signed-off-by: Roman Volosatovs <roman.volosatovs@docker.com>

integration/container/container_test.go

@@ -19,6 +19,7 @@ func TestContainerInvalidJSON(t *testing.T) {
 	}
 
 	for _, ep := range endpoints {
+		ep := ep
 		t.Run(ep, func(t *testing.T) {
 			t.Parallel()
 

integration/network/network_test.go

@@ -72,6 +72,7 @@ func TestNetworkInvalidJSON(t *testing.T) {
 	}
 
 	for _, ep := range endpoints {
+		ep := ep
 		t.Run(ep, func(t *testing.T) {
 			t.Parallel()
 
@@ -105,6 +106,7 @@ func TestNetworkList(t *testing.T) {
 	}
 
 	for _, ep := range endpoints {
+		ep := ep
 		t.Run(ep, func(t *testing.T) {
 			t.Parallel()
 

integration/plugin/common/plugin_test.go

@@ -36,6 +36,7 @@ func TestPluginInvalidJSON(t *testing.T) {
 	endpoints := []string{"/plugins/foobar/set"}
 
 	for _, ep := range endpoints {
+		ep := ep
 		t.Run(ep, func(t *testing.T) {
 			t.Parallel()
 

integration/volume/volume_test.go

@@ -110,6 +110,7 @@ func TestVolumesInvalidJSON(t *testing.T) {
 	endpoints := []string{"/volumes/create"}
 
 	for _, ep := range endpoints {
+		ep := ep
 		t.Run(ep, func(t *testing.T) {
 			t.Parallel()