go1.7: use TLS renegotiation, rm stdlib forks

Go 1.7 introduces TLS renegotiation: golang/go@af125a5

Removing our net/http and crypto/tls forks and just using Renegotation field
in the crypto/tls.Config field of the net/http.Client of the ./management/**
packages. (Fixes #90)

Should be merged once go1.7 stable is out and preferably like 1 month later.
If the customers of the ./management/ package are not vendoring the SDK and using
go versions prior to 1.7, they will get a compilation error.

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>