Automatic merge from submit-queue
Fixes panic on round tripper when TLS under a proxy
When under a proxy with a valid cert from a trusted authority, the `SpdyRoundTripper` will likely not have a `*tls.Config` (no cert verification nor `InsecureSkipVerify` happened), which will result in a panic. So we have to create a new `*tls.Config` to be able to create a TLS client right after. If `RootCAs` in that new config is nil, the system pool will be used.
@ncdc PTAL
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