Most tests that can start rabbitmq nodes have some chance of
flaking. Rather than chase individual flakes for now, this commit
changes the default (though it can still be overriden, as is the case
for config_scheme_SUITE in many places, since I have yet to see that
particular suite flake).
Adds WORKSPACE.bazel, BUILD.bazel & *.bzl files for partial build & test with Bazel. Introduces a build-time dependency on https://github.com/rabbitmq/bazel-erlang