oo-iptables-port-proxy: Rewrite getaddr

Clean up the getaddr command to use pure Bash with only one fork and
simpler (and hopefully more reliable) parsing.
oo-iptables-port-proxy: getaddr: check ipaddr

Check that ipaddr is not empty in getaddr and report a helpful error
message if it is.

This commit fixes bug 1121200.
Merge pull request #5622 from Miciah/bug-1121200-oo-iptables-port-proxy-getaddr-check-ipaddr

Merged by openshift-bot