Switch to stretchr/testify / mockery for mocks

testify is used throughout the codebase; this switches mocks from
gomock to testify with the help of mockery for code generation.

Handlers and mocks in test/utils/oidc are moved to a new package:
mockery operates package by package, and requires packages to build
correctly; test/utils/oidc/testserver.go relies on the mocks and fails
to build when they are removed. Moving the interface and mocks to a
different package allows mockery to process that package without
having to build testserver.go.

Signed-off-by: Stephen Kitt <skitt@redhat.com>

pkg/kubelet/cm/container_manager_linux_test.go

@@ -27,7 +27,6 @@ import (
 	"time"
 
 	cadvisorapiv2 "github.com/google/cadvisor/info/v2"
-	"go.uber.org/mock/gomock"
 
 	"github.com/opencontainers/runc/libcontainer/cgroups"
 	"github.com/stretchr/testify/assert"
@@ -177,17 +176,13 @@ func TestSoftRequirementsValidationSuccess(t *testing.T) {
 func TestGetCapacity(t *testing.T) {
 	ephemeralStorageFromCapacity := int64(2000)
 	ephemeralStorageFromCadvisor := int64(8000)
-	mockCtrl := gomock.NewController(t)
-	defer mockCtrl.Finish()
-	mockCtrlError := gomock.NewController(t)
-	defer mockCtrlError.Finish()
 
-	mockCadvisor := cadvisortest.NewMockInterface(mockCtrl)
+	mockCadvisor := cadvisortest.NewMockInterface(t)
 	rootfs := cadvisorapiv2.FsInfo{
 		Capacity: 8000,
 	}
 	mockCadvisor.EXPECT().RootFsInfo().Return(rootfs, nil)
-	mockCadvisorError := cadvisortest.NewMockInterface(mockCtrlError)
+	mockCadvisorError := cadvisortest.NewMockInterface(t)
 	mockCadvisorError.EXPECT().RootFsInfo().Return(cadvisorapiv2.FsInfo{}, errors.New("Unable to get rootfs data from cAdvisor interface"))
 	cases := []struct {
 		name                                 string