BUG/MEDIUM: lua-thread: some parts must be initialized once

BUG/MEDIUM: lua-thread: some parts must be initialized once

Lua dedicated TCP, HTTP and SSL socket and proxies must be initialized
once. Right now, they are initialized from the Lua init state, but since
commit 59f11be43 ("MEDIUM: lua-thread: Add the lua-load-per-thread
directive") this function is called one time per lua context. This
caused some fields to be cleared and overwritten, and pre-allocated
object to be lost. This is why the address sanitizer detected memory
leaks from the socket_ssl server initialization.

Let's move all the state-independent part of the function to the
hlua_init() function to avoid this.

No backport is needed, this is only 2.4-dev.