Revert helm to 2.14.3

- Related to: helm/helm#6718

Downgrading to 2.14.3 and forcing tillers to downgrade will allow fresh
installs without needing to refactor all the consuming code that invokes
`helm upgrade --install`

Dockerfile

@@ -7,7 +7,7 @@ FROM vaporio/foundation:latest
 ARG TF_SEMVER=0.12.12
 ENV TF_VERSION=${TF_SEMVER}_linux_amd64
 ENV CLOUD_SDK_VERSION=267.0.0
-ENV HELM_VERSION=v2.15.0
+ENV HELM_VERSION=v2.14.3
 ENV KUBECTL_VERSION=v1.16.0
 ENV HELMFILE_VERSION=v0.87.0
 ENV VELERO_VERSION=v1.1.0