Build update to support specifying repo at queue time (#85)

Author: MichaelSimons

.vsts-pipelines/jobs/build-images.yml

@@ -25,9 +25,7 @@ jobs:
       --username $(acr.userName)
       --password $(BotAccount-dotnet-docker-acr-bot-password)
       --registry-override $(acr.server)
-      --repo-prefix $(repoPrefix)
-      $(imageBuilder.queueBuildArgs)
-    repoPrefix: public/
+      --repo-prefix $(publishRepoPrefix)
   steps:
   - template: ../steps/cleanup-docker-linux.yml
     parameters:
@@ -38,7 +36,7 @@ jobs:
       docker run
       --rm
       -v /var/run/docker.sock:/var/run/docker.sock
-      -e DOCKER_REPO=$(acr.server)/($repoPrefix)dotnet-buildtools/prereqs
+      -e DOCKER_REPO=$(acr.server)/$(publishRepoPrefix)dotnet-buildtools/prereqs
       $(dockerArmRunArgs)
       $(imageBuilderTag)
       $(imageBuilderArgs)