Experimental asset sync does not honor asset_roles during sync

With the `experimental_asset_sync` feature enabled for a given app, the `precompile_assets` phase has two modes of operation: compiling assets and reusing assets.

Things work as expected when the deploy follows the "reuse" branch, but not when the deploy follows the "compile" branch.

## Expected Behavior ##

Whether assets are reused or compiled, each instance that matches the `asset_roles` configured for the application will receive direction to either sync the new assets or reuse the previous build's assets, but no other instances receive any direction.

## Actual Behavior ##

When assets are reused, each instance that matches the `asset_roles` configured for the application are directed to reuse the previous build's assets.

However, when assets are compiled, each instance that is not `app_master` is directed to sync the assets from `app_master`, including those not matching the configured `asset_roles`.

## Affected Versions ##

Presumably all, but definitely 2.6.17 and 2.6.19, the two most recent published releases.

## Aside ##

This bug was discovered by a single customer that relies on the incorrect behavior. They have added the proper `asset_roles` configuration to ensure that their desired behavior continues if this bug should be squashed.