cleanup auto-generated /tmp/ files after kube-down

[sonyafenge]

What happened:
when run ./cluster/kube-up.sh, got error: "./cluster/../cluster/../cluster/gce/util.sh: line 2970: /tmp/master_reserved_ip.txt: Permission denied". after I manually rm this file, I can get kube-up running successfully.
when run ./test/kubemark/start-kubemark.sh, there is no response. and no any log out.
What you expected to happen:
no error popup for kube-up.sh and run successfully for start-kubemark.sh
How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

Environment:

• Arktos version (use kubectl version):

23d3fb99278 (HEAD -> master, upstream/master) Make perf scripts ready for insecure scale-out tests (#964)

• Cloud provider or hardware configuration:
• OS (e.g: cat /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Network plugin and version (if this is a network-related bug):
• Others: