Read cookie file from git-remote-persistent-https if applicable

git-remote-persistent-https proxy implementations may pass cookie file
configuration to git-remote-https. When fetching bundles for
persistent-http(s) URLs, use the -print_config flag (if supported) to
extract this information from the proxy binary and pass it to curl,
overriding http.cookiefile from .gitconfig.

This adds a few ms overhead per clone.bundle fetch, which should be
acceptable since it happens only on the initial clone, which takes
much longer anyway.

Change-Id: I03be8ebaf8d3005855d33998cd8ecd412e8ec287