expose HTTP.request config to mirror_tarball

[skyzh]

HTTP.jl allows a lot of customizations. If this config can be exposed to mirror_tarball function, we can better adjust parameters to achieve faster synchonization.

HTTP.request("GET", "http://httpbin.org/ip"; retries=4, cookies=true)
HTTP.get("http://s3.us-east-1.amazonaws.com/"; aws_authorization=true)
conf = (readtimeout = 10,
        pipeline_limit = 4,
        retry = false,
        redirect = false)
HTTP.get("http://httpbin.org/ip"; conf..)
HTTP.put("http://httpbin.org/put", [], "Hello"; conf..)

[johnnychen94]

added in 1c25e0add20ccdc618f8689ce4d744dd4d5188f9