This splits `prepare` into 3 methods so that the code that sets
default omnibus config can be called in the Praefect scenario
without also attempting to pull the docker image again.

Set default omnibus config in Praefect scenario

See merge request !449

Tomislav Nikić authored May 05, 2020 and Mark Lapierre committed May 05, 2020

Constructing a simple Gitaly HA setup using two Gitaly nodes, one
Praefect node and one standard Gitlab instance.

Construct a Gitaly HA setup

See merge request !398