Fix Docker test to wait fixed time (#5858)
Fix Docker test to wait fixed time (#5858)

## What is the goal of this PR?

Waiting for Grakn port to be open didn't prove to be the best strategy: test executing queries failed even though the port was already opened. Instead, we're opting in to wait a fixed amount of time. This strategy is also using in [`docs`](https://github.com/graknlabs/docs/blob/316b27ba1bdc69e6bbd0c6af8645320b2a492144/.circleci/config.yml#L41) where Grakn server is also started.

## What are the changes implemented in this PR?

Wait a fixed amount of time (30s) which should be plenty for Grakn to bootup.
graknlabs/grakn,graknlabs/grakn,lolski/grakn,lolski/grakn,graknlabs/grakn,graknlabs/grakn,lolski/grakn,lolski/grakn