This change fixes a regression regarding the way we fetch the Review List

resource and create reviews using it. Previously, we would fetch this from the

Root List resource, which would then get the Review List resource from the

appropriate Review Request resource. In Review Board 5.0, we introduced a Root

Review List resource, so now this gets returned from the Root List resource

instead. This Root Review List resource does not support the POST method, so

this broke review draft creation. To fix this, we update the code to fetch the

Review List resource directly from the Review Request resource instead of

fetching it from the Root List resource.
The codebase was also checked to see if there are any regressions from

introducing the Root Diff Comment List resource, Root File Attachment

Comment List resource and Root General Comment List resource, which were

also introduced in Review Board 5.0. No regressions for these were found.
These changes are also compatible with Review Board 4.x.

Manually tested the rbt review and rbt status-update commands.
Ran unit tests.