Add wait flag to iptables

Fixes #1573
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Update integration tests with --net flag
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Update ip test to parse new output
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Merge pull request #5998 from crosbymichael/iptables-wait

Add wait flag to iptables
Merge pull request #6015 from crosbymichael/update-test-flags

Update integration tests with --net flag
Add specific branch of jpetazzo's busybox to clone from so we can assume nice things about it

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Simplify "adduser" in the Dockerfile to use the more scripting-friendly "useradd"

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)