ProxyFromEnvVars provides an alternative to http.ProxyFromEnvironment
since it is being initialized only once and that happens by k8s before
proxy settings was obtained from the cluster.
While this is no issue for k8s client, it prevents any out-of-cluster
traffic from using the proxy.

By providing implementation of that method, we allow to use env-vars
set for the pod based on the cluster-wide-proxy.

Signed-off-by: Moti Asayag <masayag@redhat.com>