e2e docker+cni and curl google.com

[stealthybox]

Changes:

• Add e2e tests for internet connectivity
• Refactor e2e and add docker+cni

TestCurlWithDockerAndDockerBridge passes with sleep 0
TestCurlWithDockerAndCNI fails the curl with sleep 0
TestCurlWithDockerAndCNISLeep2 curl succeeds 🙃

It's very reproducible.
Setting up CNI appears to be latent.
This is very undesirable -- we should fix it. (opened #423)

sudo IGNITE_E2E_HOME=$(pwd) $(which go) test ./e2e/. -count 1 -run TestCurlWithDocker | egrep -i 'fail|assert'                                                         19/09/11  6:54:12 am
time="2019-09-11T06:54:22-06:00" level=fatal msg="failed to dial: dial tcp 172.18.0.102:22: connect: connection refused"
--- FAIL: TestCurlWithDockerAndCNI (3.72s)
    run_test.go:131: assertion failed: error is not nil: exit status 1: curl should not fail: ["/home/stealthybox/Repos/ignite/bin/ignite" "--runtime=docker" "--network-plugin=cni" "exec" "e2e_test_curl_docker_and_cni" "curl" "google.com"]
    run_test.go:114: assertion failed: error is not nil: exit status 1: vm removal should not fail: ["/home/stealthybox/Repos/ignite/bin/ignite" "--runtime=docker" "--network-plugin=cni" "rm" "-f" "e2e_test_curl_docker_and_cni"]
--- FAIL: TestCurlWithDockerAndCNISleep2 (4.97s)
    run_test.go:114: assertion failed: error is not nil: exit status 1: vm removal should not fail: ["/home/stealthybox/Repos/ignite/bin/ignite" "--runtime=docker" "--network-plugin=cni" "rm" "-f" "e2e_test_curl_docker_and_cni_sleep2"]
FAIL
FAIL	github.com/weaveworks/ignite/e2e	14.554s
FAIL

[chanwit]

We need these test cases to help tackling the current CNI issues.
LGTM