Fixes #342, cleanup netns after test suite

[smarkm]

Fixes #342, please also reference #373

[mars1024]

/lgtm

[dcbw]

@smarkm looks good, but can you rebase onto containernetworking/plugins git master to get rid of the merge commit? Basically, you can add containernetworking/plugins as a git remote:

git remote add upstream git@github.com:containernetworking/plugins.git
git fetch upstream
git rebase upstream/master

and then push the PR again (you may need to git push -f to overwrite your existing PR branch, which is fine).

Thanks!

[smarkm]

@dcbw thanks for your information!

[jellonek]

lgtm

[squeed]

awesome, thanks!