* test: stub out ipfs interactions in http injection tests

This makes running the tests faster as we do no network operations,
nor do we wait for ports to open, etc.

Functionality covered by the tests is also covered by the interface
tests so there is no testing gap.

Removes use of ipld by the importer, instead using the block api directly.

This allows use by implementations that have only completed low-level APIs
and also makes importing ever so slightly faster by not serializing nodes
twice while adding them to the block store.

Response streams from DHT operations contain lots of message types, one of which is 'Error', but they are emitted for all sorts of reasons, failing to dial peers, etc and valid responses can arrive after several errors.

The change here is to ignore error messages sent by the remote node as they do not indicate that the request has failed.

Fixes #2991

 - interface-ipfs-core@0.134.1
 - ipfs-http-client@44.0.1
 - ipfs@0.43.1

It misreports coverage numbers because it doesn't take into account
that only the tests of changed modules and their dependents run in
each build, it only reports coverage of node tests, it marks every
PR as failed build checks yet we merge them anyway.

We can re-enable it when we solve the problems above.

Somewhere along the line we stopped passing headers to the underlying
request library which means people can't use http auth etc to try to
secure their API servers.

Fixes #3017

 - interface-ipfs-core@0.134.2
 - ipfs-core-utils@0.2.1
 - ipfs-http-client@44.0.2
 - ipfs@0.43.2