MINOR: hlua/event_hdl: expose SERVER_CHECK event

Exposing SERVER_CHECK event through the lua API.

New lua class named ServerEventCheck was added to provide additional
data for SERVER_CHECK event.

Lua documentation was updated accordingly.
diff --git a/doc/lua-api/index.rst b/doc/lua-api/index.rst
index 8a82a16..d790c6b 100644
--- a/doc/lua-api/index.rst
+++ b/doc/lua-api/index.rst
@@ -948,6 +948,9 @@
     * **SERVER_UP**: when a server state goes from DOWN to UP
     * **SERVER_STATE**: when a server state changes
     * **SERVER_ADMIN**: when a server administrative state changes
+    * **SERVER_CHECK**: when a server's check status change is reported.
+      Be careful when subscribing to this type since many events might be
+      generated.
 
    .. Note::
      Use **SERVER** in **event_types** to subscribe to all server events types
@@ -1541,6 +1544,13 @@
   .. Note::
      Only available for SERVER_ADMIN event
 
+.. js:attribute:: ServerEvent.check
+
+  A :ref:`server_event_checkres_class`
+
+  .. Note::
+     Only available for SERVER_CHECK event
+
 .. _server_event_checkres_class:
 
 ServerEventCheckRes class