It was previously possible to link a GCP account to another
user's GitLab account by having them visit the callback URL,
as there was no check that they were the initiator of the
request.
We now reject the callback unless the state parameter
matches the one added to the initiating user's session.
Updates specs to use new rails5 format.
The old format:
`get :show, { some: params }, { some: headers }`
The new format:
`get :show, params: { some: params }, headers: { some: headers }`
