hack/tests: make more gce options configurable
hack/tests: make more gce options configurable

kubernetes-incubator/bootkube,ericchiang/bootkube,diegs/bootkube,dghubble/bootkube,ericchiang/bootkube,hongchaodeng/bootkube,hongchaodeng/bootkube,kubernetes-incubator/bootkube,dghubble/bootkube,diegs/bootkube,diegs/bootkube,hongchaodeng/bootkube,kubernetes-incubator/bootkube,dghubble/bootkube,ericchiang/bootkube