Also test against go-ipfs

[alanshaw]

trafficstars

Currently tests only run against js-ipfs. We should run against go-ipfs also so that proxying for features available in go-ipfs that are not yet available in js-ipfs can be tested.

For example, currently js-ipfs doesn't support MFS - the tests exist in interface-ipfs-core but are skipped when testing against a js-ipfs node.

We need:

• [x] node -> js-ipfs-api -> go-ipfs
• [ ] browser -> js-ipfs-api -> go-ipfs