Fix all invalid IPs in the iptables nat file

Modify fixaddr to check every entry in the nat rules file instead of
just looking at the last entry.
Fix race condition in secure_cartridge

Remove Dir.chdir and use absolute file paths instead because chdir is
not thread-safe.

Bug 998345
Bug 1025043
Merge pull request #4092 from ncdc/fix-all-invalid-iptables-ips

Merged by openshift-bot
Merge pull request #4091 from ncdc/fix-secure-cartridge-race-condition

Merged by openshift-bot