Merge the tip of origin/release/proposed/2019.2.0 into origin/release/2019.2.0

f2e0ec85 Bump Prometheus to 2019.2.23
1b806c3d Update docker images
5a6b3398 Migrate git mirroring source data to cluster model

Change-Id: Iaeb9daa677798fe5bbfcf7e5de14b2cdc760c99d