Set shell options for reliability.

Tweak a few other small things in our shell scripts.

cluster/kube-push.sh

@@ -19,8 +19,9 @@
 # This will find the release tar, cause it to be downloaded, unpacked, installed
 # and enacted.
 
-# exit on any error
-set -e
+set -o errexit
+set -o nounset
+set -o pipefail
 
 KUBE_ROOT=$(dirname "${BASH_SOURCE}")/..
 source "${KUBE_ROOT}/cluster/kube-env.sh"