upgrade weave, flannel, kubernetes and base AMI image

[nonsense]

Fixes testground/testground#1128

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This PR is upgrading Kubernetes (based on kops 1.18.2 => Kubernetes v1.8.10), our base AMI image (now based on ubuntu-focal-20.04) with all the bundled docker images, and Weave (to v2.7.0), since we haven't upgraded many of these for many months.

It is also fixing a few broken env vars from the previous commit.

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TODO:

• upgrade flannel (it is done as part of kops, so will submit PR upstream).
• figure out why blackhole rules by sidecar do not play well with the upgraded deps.
• document that default db in influxdb is no longer created automatically ("testground")

[nonsense]

This is ready for review - nothing really interesting is going on here.

For some reason the new dependencies do not work with the blackhole functionality we have in the Testground sidecar - we are adding blackhole rules for larger parts of the network and then we are supposed to open routes to influxdb and redis (denoted as services in the sidecar), but the routes to these services are sometimes missing.

I will investigate what's the problem there, and make sure our test plans work well with the new versions.

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The reason I am upgrading all of these is because many bugs got fixed on Weave and Kubernetes side, and TaaS does suffer from some of them.

[hacdias]

LGTM!