fix(adapter-node-http): Fix unhandled rejection if connection fails

[dustinsoftware]

An unhandled promise rejection was thrown if a socket could not be opened,
which prevents handling the error gracefully in a consuming app.

First of all, thanks for building this library! I'm exposing a HTTP API on top of it here and it's working pretty well. However..

I'm running into a crash when polly can't connect to an API (port isn't open, for instance).

In my app, I'm tearing down the process if there are any unhandled promise rejections by using:

process.on('unhandledRejection', exception => {
	throw exception;
});

I had to fix promise rejection handling in a few places, but it works properly now. I've confirmed that this fix allows polly-proxy to return a graceful HTTP 500 from the express instance instead of crashing the app, but am unsure the best way to add a test for this type of bug.

[dustinsoftware]

Looks like CI passed for Node 8 and 10, but failed for 6 during package restore 🤷‍♂️

[dustinsoftware]

I've added a test that verifies the expected behavior in polly-proxy on the test-updates branch.

To repro with that project:
yarn build && yarn test:ci

To verify this fix:
yarn link @pollyjs/adapter-node-http
yarn link @pollyjs/core
yarn build && yarn test:ci

I'm not sure that adding promise.catch(() => {}) is the best solution here, although it doesn't seem to negatively affect consumers (such as flush)

[dustinsoftware]

FWIW I was able to successfully hack around the issue in deferred-promise.js but ended up forking adapter-node-http until we can get a fix in :)

dustinsoftware/polly-proxy@c558c6c

[offirgolan]

Thanks for submitting these fixes @dustinsoftware! The changes look good but im skeptical on one part.