s4:lib/http: use http_conn in http_send_request_send() and http_read_response_send()

s4:lib/http: use http_conn in http_send_request_send() and http_read_response_send()

Works, tested with

  $ bin/smbtorture -W RIVERSIDE --realm=RIVERSIDE.SITE -s /dev/null \
    -U Administrator%Passw0rd \
    ncacn_http:10.10.11.164[HttpProxy=10.10.11.164:593,HttpUseTls=false,HttpAuthOption=basic,HttpConnectOption=UseHttpProxy] \
    rpc.epmapper.epmapper.Lookup_simple

I get an ACCESS_DENIED error, but I get it over HTTP. :)

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Samuel Cabrero <scabrero@suse.de>