Launching virt-manager in ssh X11 forwarded session gives "RuntimeError: could not open display"

Issue

• # virt-manager gives error as RuntimeError: could not open display when it is executed after connecting to host via ssh with X11 forwarding.

  # virt-manager 
  Traceback (most recent call last):
   File "/usr/share/virt-manager/virt-manager.py", line 383, in <module>
     main()
   File "/usr/share/virt-manager/virt-manager.py", line 286, in main
     raise gtk_error
  RuntimeError: could not open display
  

• Seeing logs as: [abrt] virt-manager-0.9.0-18.el6: virt-manager.py:286:main:RuntimeError: could not open display on the system.