How to resolve "enter the password for credential storage" issue?
I could now install the certificate. I had to disable pattern screen lock and try installing certificate again. This time it asked me to setup security - pin or password. 



That I did and cert got installed. Got the solution from android central forum.

http://forums.androidcentral.com/google-nexus-7-tablet-2012/301151-credential-storage.html

I guess that thread is for VPN but same solution works for Wifi certs as well. Please do add if anyone has any additional info on this or workaround.