do not hardcode the path

rootfs/etc/nginx/lua/balancer/sticky.lua

@@ -41,7 +41,7 @@ local function set_cookie(self, value)
   ok, err = cookie:set({
     key = self.cookie_name,
     value = value,
-    path = "/",
+    path = ngx.var.location_path,
     domain = ngx.var.host,
     httponly = true,
   })

rootfs/etc/nginx/lua/test/balancer/sticky_test.lua

@@ -40,7 +40,7 @@ end
 
 describe("Sticky", function()
   before_each(function()
-    mock_ngx({ var = {} })
+    mock_ngx({ var = { location_path = "/" } })
   end)
 
   after_each(function()
@@ -117,7 +117,7 @@ describe("Sticky", function()
             set = function(self, payload)
               assert.equal(payload.key, test_backend.sessionAffinityConfig.cookieSessionAffinity.name)
               assert.equal(payload.value, util[test_backend_hash_fn .. "_digest"](test_backend_endpoint))
-              assert.equal(payload.path, "/")
+              assert.equal(payload.path, ngx.var.location_path)
               assert.equal(payload.domain, nil)
               assert.equal(payload.httponly, true)
               return true, nil