Share test utility across all integration tests

[arboleya]

We have a few testing utilities scattered around, some very repetitive. We should try to condense them all in a single place (packages/utils) to reduce the noise and improve maintenance.

This seems like a good start ^(usage) — although we need more options and flexibility, I like the simplicity of it.

We can draw inspiration and requirements from fuel-gauge and similar integration tests.

[maschad]

Related #1751

[arboleya]

I briefly spoke with @nedsalk about the location of test utilities (wrt to #1356), and it might not be that easy to move everything around like this. This is something we need to talk about.

[arboleya]

Closing in favor of:

• Integrate launchTestNode with fuel-gauge  #1820