core: Add ap_create_connection() to create a server or client/proxy connection.

core: Add ap_create_connection() to create a server or client/proxy connection.

c->outgoing shouldn't be set by mod_ssl, ap_create_connection() allows that
and this commit also replaces all the calls to ap_run_create_connection() in
mod_proxy modules (not in the MPMs which create incoming connections only).

* include/http_connection.h, server/connection.c:
  Declare and implement ap_create_connection().

* modules/proxy/proxy_util.c, modules/proxy/mod_proxy_connect.c,
  modules/proxy/mod_proxy_ftp.c:
  Use ap_create_connection() instead of ap_run_create_connection(), and don't
  provide a connection_id a scoreboard handle for outgoing connection.

* server/log.c(do_errorlog_default):
  Use c->outgoing instead of c->sbh to determine if it's a "client" or "remote"
  connection.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1893184 13f79535-47bb-0310-9956-ffa450edef68