internal: rework replicasets schema reload

This patch is the groundwork for vshard groups and custom routers
support.

After this patch, schema reload works per vshard router object.

Test runs have shown that this patch do not affects the performance of
crud requests.

Part of #44

crud/common/schema.lua

@@ -49,24 +49,30 @@ local function call_reload_schema(replicasets)
     return true
 end
 
-local reload_in_progress = false
-local reload_schema_cond = fiber.cond()
+local reload_in_progress = {}
+local reload_schema_cond = {}
 
-local function reload_schema(replicasets)
-    if reload_in_progress then
-        if not reload_schema_cond:wait(const.RELOAD_SCHEMA_TIMEOUT) then
+local function reload_schema(vshard_router)
+    local replicasets = vshard_router:routeall()
+    local vshard_router_name = vshard_router.name
+
+    if reload_in_progress[vshard_router_name] == true then
+        if not reload_schema_cond[vshard_router_name]:wait(const.RELOAD_SCHEMA_TIMEOUT) then
             return nil, ReloadSchemaError:new('Waiting for schema to be reloaded is timed out')
         end
     else
-        reload_in_progress = true
+        reload_in_progress[vshard_router_name] = true
+        if reload_schema_cond[vshard_router_name] == nil then
+            reload_schema_cond[vshard_router_name] = fiber.cond()
+        end
 
         local ok, err = call_reload_schema(replicasets)
         if not ok then
             return nil, err
         end
 
-        reload_schema_cond:broadcast()
-        reload_in_progress = false
+        reload_schema_cond[vshard_router_name]:broadcast()
+        reload_in_progress[vshard_router_name] = false
     end
 
     return true
@@ -92,7 +98,7 @@ function schema.wrap_func_reload(func, ...)
         end
 
         local vshard_router = vshard.router.static
-        local ok, reload_schema_err = reload_schema(vshard_router:routeall())
+        local ok, reload_schema_err = reload_schema(vshard_router)
         if not ok then
             log.warn("Failed to reload schema: %s", reload_schema_err)
             break