fix: replace instanceof Promise checks with thennable checks

[M-TGH]

Issue #, if available: No issue, came up in #98 (comment).

Description of changes: Replaces 2 instanceof Promise checks to instead check if .then is a function.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

If preferred I can merge this into the feat/support-pool-get-connection branch.

Wasn't too sure on a way to add tests for this, so refrained on adding them for now. Let me know if you have any ideas.

[chrisradek]

In this case, if the existing tests pass I'm fine with merging. This change is more to protect us in case mysql supports providing a customer Promise implementation in the future (if it doesn't already).

[chrisradek]

@M-TGH
Thank you for the contribution! Merging!

[darcoli]

We seem to be hitting a situation where connection is undefined and then everything else fails because now all conditions in the if statements try to read property then of undefined. I believe there should be an additional guard for such cases in all places where this was changed. (We incurred this issue with typeorm and mysql with aws-xray-sdk 2.3.1 within aws lambda)

Full exception:

TypeError: Cannot read property 'then' of undefined
  File "/var/task/dist/handler.js", line 89720, col 16, in Pool.patchedGetConnection [as getConnection]
    if (result.then instanceof Function) return result.then(patchObject);
  File "/var/task/dist/handler.js", line 5255, col 18, in null.<anonymous>
    pool.getConnection(function (err, connection) {
  File "/var/task/dist/handler.js", line 81363, col 18, in new WrappedPromise
    executor.apply(context, args);
  File "/var/task/dist/handler.js", line 5252, col 16, in MysqlDriver.module.exports.MysqlDriver.createPool
    return new Promise(function (ok, fail) {
  File "/var/task/dist/handler.js", line 4765, col 51, in MysqlDriver.<anonymous>
    return [4 /*yield*/, this.createPool(this.createConnectionOptions(this.options, this.options))];
  File "/var/task/dist/handler.js", line 209, col 23, in step
    op = body.call(thisArg, _);
  File "/var/task/dist/handler.js", line 190, col 53, in Object.next
    function verb(n) { return function (v) { return step([n, v]); }; }
  File "/var/task/dist/handler.js", line 183, col 71, in null.<anonymous>
    step((generator = generator.apply(thisArg, _arguments || [])).next());
  File "/var/task/dist/handler.js", line 81363, col 18, in new WrappedPromise
    executor.apply(context, args);
  File "/var/task/dist/handler.js", line 179, col 12, in Module.__awaiter
    return new (P || (P = Promise))(function (resolve, reject) {
  File "/var/task/dist/handler.js", line 4750, col 24, in MysqlDriver.module.exports.MysqlDriver.connect
    return tslib_1.__awaiter(this, void 0, void 0, function () {
  File "/var/task/dist/handler.js", line 43526, col 58, in Connection.<anonymous>
    return [4 /*yield*/, this.driver.connect()];
  File "/var/task/dist/handler.js", line 209, col 23, in step
    op = body.call(thisArg, _);
  File "/var/task/dist/handler.js", line 190, col 53, in Object.next
    function verb(n) { return function (v) { return step([n, v]); }; }
  File "/var/task/dist/handler.js", line 183, col 71, in null.<anonymous>
    step((generator = generator.apply(thisArg, _arguments || [])).next());
  File "/var/task/dist/handler.js", line 81363, col 18, in new WrappedPromise
    executor.apply(context, args);
  File "/var/task/dist/handler.js", line 179, col 12, in Module.__awaiter
    return new (P || (P = Promise))(function (resolve, reject) {
  File "/var/task/dist/handler.js", line 43518, col 24, in Connection.module.exports.Connection.connect
    return tslib_1.__awaiter(this, void 0, void 0, function () {
  File "/var/task/dist/handler.js", line 155846, col 65, in ConnectionManager.get
    return connection.isConnected ? connection : connection.connect();
  File "/var/task/dist/handler.js", line 155960, col 57, in CommandScheduleService.runScheduledCommands
    const connection = await this.connectionManager.get();
  File "/var/task/dist/handler.js", line 56480, col 27, in module.exports.exports.commandScheduleRunner.handler_1.sentryfy
    await scheduleService.runScheduledCommands();
  File "/var/task/dist/handler.js", line 42585, col 25, in null.<anonymous>
    const promise = handler(event, context, callback);

[chrisradek]

@darcoli
Thank you for reporting that issue. I'll create an update those conditions to include an existence check before checking for then.