BUG/MEDIUM: lua: dead lock when Lua tasks are trigerred

BUG/MEDIUM: lua: dead lock when Lua tasks are trigerred

When a task is created from Lua context out of initialisation,
the hlua_ctx_init() function can be called from safe environement,
so we must not initialise it. While the support of threads appear,
the safe environment set a lock to ensure only one Lua execution
at a time. If we initialize safe environment in another safe
environmenet, we have a dead lock.

this patch adds the support of the idicator "already_safe" whoch
indicates if the context is initialized form safe Lua fonction.

thank to Flakebi for the report

This patch must be backported to haproxy-1.9 and haproxy-1.8