SOLVED. Found the problem.

Step 1: make a web server

$ echo "complex world" | nc -l 80 # run a webserver

Step 2: make a https server connects to step 1

$ pgrep -f stunnel | xargs kill -9; stunnel

Step 3: verify SSL is working of step 2

$ openssl s_client -ssl3 -connect server1.com:443

lot of data.. and SSL handshake has read 3029 bytes and written 354 bytes means successfully installed

Step 4: final 

$ curl -v "https://server1.com" 

or

$ google-chrome "https://server1.com"

i get the output from webserver and the url stays in https:// 

Summary: Google App Engine is pain (someone please fix it or report Google, cause Google App engine is now became very popular but its pain when you use it with stunnel + apache). They have a redirect which cause the SSL/HTTPS not working  it was confusing if stunnel issue or apache issue. In apache you can do the same by following this which proves that Google App Engine is EVIL for https.

Apache2, in CentOS 6.4:

Step 2: same as above stunnel but if you want without stunnel and use apache then you need as below:

$ cat /etc/httpd/conf.d/ssl.conf