Fix Docker image test (#5846)
Fix Docker image test (#5846)

## What is the goal of this PR?

Currently, `test-assembly-docker` depends on `curl` built in a specific way (with HTTP/2 support). This is not always the case, so test might silently timeout (underlying `curl` command fails with `Received HTTP/0.9 when not allowed`)

## What are the changes implemented in this PR?

Refactor `test/assembly/docker.py` to use native Python `socket` module to test for Grakn readiness
graknlabs/grakn,graknlabs/grakn,lolski/grakn,lolski/grakn,lolski/grakn,lolski/grakn,graknlabs/grakn,graknlabs/grakn