Update Bazel to 0.22 and LLVM/clang to 7.

[PiotrSikora]

Signed-off-by: Piotr Sikora [email protected]

[sebastienvas]

@utka once this is merged, you would need to build the new image, and update the proxy jobs in https://github.com/istio/test-infra/blob/master/prow/cluster/jobs/istio/proxy/istio.proxy.master.yaml#L4.

The proxy jobs haven't been updated to use podutils, so we should do so, and while we do that, we should create an image for proxy, in this dir https://github.com/istio/test-infra/tree/master/docker/istio

[PiotrSikora]

/assign @sebastienvas

[wenchenglu]

/lgtm
/approve

[istio-testing]

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