Add a verbosity concept to kubernetes scripts

The KUBE_VERBOSE environment variable sets the verbosity level to
use. Log messages can specify a verbosity by setting the V
variable. e.g.

    V=2 kube::log::info foo bar

Would only print "foo bar" if $KUBE_VERBOSE >= 2.

hack/make-rules/build.sh

@@ -21,6 +21,7 @@ set -o nounset
 set -o pipefail
 
 KUBE_ROOT=$(dirname "${BASH_SOURCE}")/../..
+KUBE_VERBOSE="${KUBE_VERBOSE:-1}"
 source "${KUBE_ROOT}/hack/lib/init.sh"
 
 kube::golang::build_binaries "$@"