Use "ip netns exec" instead of "nsenter" to handle pod restart in network-chaos

[Calvinaud]

• Replacing the nsenter command by ip netns exec
• Updating helper pod definition to mount the hostPath /var/run/netns
• Updating Dockerfile to add ip binary to experiments/helper pod.

What this PR does / why we need it:

Updating network-chaos to use the netns instead of the procedure to inject/remove chaos so the network-chaos can handle pod restart.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #591

Special notes for your reviewer:

I think this PR will need "requires-upgrade".

Checklist:

• [X] Fixes #591
• [ ] PR messages has document related information
• [X] Labelled this PR & related issue with breaking-changes tag
• [X] PR messages has breaking changes related information
• [ ] Labelled this PR & related issue with requires-upgrade tag
• [ ] PR messages has upgrade related information
• [ ] Commit has unit tests
• [ ] Commit has integration tests
• [x] E2E run Required for the changes