richackard: Implemented the update-latest flag for gke_make

JobBuild
159
07-29 18:44
pull-kubetest2-build 1421250031368802304 1421228911991197696 1421226611159601152 1420876798920495104 1420817560915415040
pull-kubetest2-gke-up-down-multicluster 1421250031297499136 1421228911924088832 1421226611084103680 1420876798849191936 1420817560844111872
pull-kubetest2-gke-up-down-singlecluster 1421250031268139008 1421228911882145792 1421226611046354944 1420876798815637504 1420817560810557440
pull-kubetest2-verify 1421250031326859264 1421228911953448960 1421226611117658112 1420876798882746368 1420817560865083392