Integration test with publish and install

[mhofman]

endo should have an integration test similar to the one introduced in https://github.com/Agoric/agoric-sdk/pull/4236 so that we can verify that packages that would be published are usable as expected. This would prevent issues such as #1099 from slipping by.

Design

Add CI test doing at least the following:

• Package and publish to a local NPM registry such as verdaccio
• Checkout a template project, with endo packages as * semver dependencies (making sure no yarn.lock is committed)
• yarn install

Alternatively, creating an empty project and yarn add endo packages might work as well.