CI: wait for repositories to clone in e2e tests
Created by: chrismwendt
Fixes flaky Percy test (reported by @sqs in https://github.com/sourcegraph/sourcegraph/pull/2755#issuecomment-473182808)
Created by: chrismwendt
Fixes flaky Percy test (reported by @sqs in https://github.com/sourcegraph/sourcegraph/pull/2755#issuecomment-473182808)