tests: made a test case more deterministic for GC.

Author: agentzh

t/129-ssl-socket.t

@@ -1439,6 +1439,8 @@ SSL reused session
 
         do
 
+        local sessions = {}
+
         for i = 1, 3 do
             local ok, err = sock:connect("iscribblet.org", 443)
             if not ok then
@@ -1454,6 +1456,8 @@ SSL reused session
                 return
             end
 
+            sessions[i] = session
+
             ngx.say("ssl handshake: ", type(session))
 
             local ok, err = sock:setkeepalive()