Integrate verification framework

Verification framework is integrated with:
  - integration tests (by default)
  - `ETCD_VERIFY=all etcdctl snapshot restore` command
  - etcd shutdown when running with `ETCD_VERIFY=all` env.

tests/integration/testing.go

@@ -22,6 +22,7 @@ import (
 	grpc_logsettable "github.com/grpc-ecosystem/go-grpc-middleware/logging/settable"
 	"go.etcd.io/etcd/client/pkg/v3/testutil"
 	"go.etcd.io/etcd/server/v3/embed"
+	"go.etcd.io/etcd/server/v3/verify"
 	"go.uber.org/zap/zapcore"
 	"go.uber.org/zap/zapgrpc"
 	"go.uber.org/zap/zaptest"
@@ -38,6 +39,9 @@ func BeforeTest(t testutil.TB) {
 
 	grpc_logger.Set(zapgrpc.NewLogger(zaptest.NewLogger(t).Named("grpc")))
 
+	// Integration tests should verify written state as much as possible.
+	os.Setenv(verify.ENV_VERIFY, verify.ENV_VERIFY_ALL_VALUE)
+
 	previousWD, err := os.Getwd()
 	if err != nil {
 		t.Fatal(err)