gRPC client methods are not patched correctly

[mayurkale22]

gRPC client methods are not patched correctly (see below sample code). This may be related to #384.

'use strict';

const { NodeTracer } = require('@opentelemetry/node');
const { SimpleSpanProcessor } = require('@opentelemetry/tracing');
const { JaegerExporter } = require('@opentelemetry/exporter-jaeger');
const tracer = new NodeTracer();
const exporter = new JaegerExporter({serviceName: 'otel',});
tracer.addSpanProcessor(new SimpleSpanProcessor(exporter));

const express = require('express');
const app = express();
const {Spanner} = require('@google-cloud/spanner');
const projectId = 'xxx';
const instanceId = 'yyy';
const databaseId = 'zzz';
const spanner = new Spanner({projectId});

// Gets a reference to a Cloud Spanner instance and database
const instance = spanner.instance(instanceId);
const database = instance.database(databaseId);

// This incoming HTTP request should be captured by Trace
app.get('/', async (req, res) => {
  // This outgoing HTTP request should be captured by Trace
  let data = '';
  try {
    const playersTable = database.table('Players');
    const query = {columns: ['email'], keySet: {all: true,},};
    const [rows] = await playersTable.read(query);
    rows.forEach(row => {
      const json = row.toJSON();
      data += json.email + '\n';
    });
    res.status(200).send(data).end();
  }
  catch (err) {
    console.error(err);
    res.status(500).end();
  }
});

// Start the server
const PORT = process.env.PORT || 8080;
app.listen(PORT, () => {
  console.log(`App listening on port ${PORT}`);
  console.log('Press Ctrl+C to quit.');
});