[feature] add h2 / spdy support

[gabrielcsapo]

What did I do?

Set up the initial pieces for serving http2 content in testem

What needs to be done

• Leverage server push to push down assets on initial load (using this.config.getServeFiles we can get all the files needed and res.push them on initial load)

[stefanpenner]

I think moving to h2 makes sense, but @gabrielcsapo some I questions (mostly to understand impact):

• how does the h2 perform relative to http1.1 given an app with many assets?
• given ^, how much does push improve ^.

[step2yeung]

+1 on Stefan's comment on performance impact.

One caveat that I think needs discussion is that the cert used by testem will be self signed certs that the browsers will likely first redirect to a warning page, which I feel could be a breaking change. (Unless we there are flags for browsers that can bypass it?)

[stefanpenner]

@step2yeung good point, could you investigate further?

[rwjblue]

Why do we have both a package-lock.json and yarn.lock?

[rwjblue]

I'm slightly concerned that this is unmaintained...

Is there any reason we can't use the built-in http2 module when present?

[gabrielcsapo]

Right yeah I am under the mind that we should be using the built in modules for this instead of using express, which has had an open RB for almost 3 years for this support.

[step2yeung]

Chrome has --allow-insecure-localhost switch to allow this, while Firefox has
network.websocket.allowInsecureFromHTTPS that can be added to the profile

But i don't think there are similar flags that is accepted by other supported browsers.