http-push: refactor curl_easy_setup madness

http-push: refactor curl_easy_setup madness

We were doing (nearly) the same thing all over the place, in slightly
different orders, different variable names, etc. Refactor most calls
into two helper functions, one for GET and one for everything else, that
do the heavy lifting leaving most callsites a lot cleaner in the
process.

Note that the setting of CURLOPT_PUT at the callsites of
curl_setup_http() which previously didn't do it (eg.
locking_available(), remote_ls()) is safe, since that
option is deprecated in libcurl in place of, and has the same effect as,
CURLOPT_UPLOAD.

Signed-off-by: Dan McGee <dpmcgee@gmail.com>
Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>