Added getClientPrincipalUser() function to extract username without domain
Added getClientPrincipalUser() function to extract username without domain

Summary:
Added getClientPrincipalUser() function to extract username without
domain

Test Plan: Tested under unittests for ncs

Reviewed By: yfeldblum@fb.com

Subscribers: alandau, bmatheny, yfeldblum, coryhill

FB internal diff: D2417478

Tasks: 7859100

Signature: t1:2417478:1441410173:64443c51ae99f998ff70bbbcafe4ad32727d72c5

getyourguide/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,Orvid/fbthrift,LinusU/fbthrift,LinusU/fbthrift,Orvid/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,sinjar666/fbthrift,getyourguide/fbthrift,sinjar666/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,sinjar666/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,facebook/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,Orvid/fbthrift,LinusU/fbthrift,Orvid/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,sinjar666/fbthrift,Orvid/fbthrift,LinusU/fbthrift,facebook/fbthrift,sinjar666/fbthrift,Orvid/fbthrift,Orvid/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,sinjar666/fbthrift,getyourguide/fbthrift,facebook/fbthrift,Orvid/fbthrift,Orvid/fbthrift,LinusU/fbthrift,LinusU/fbthrift,Orvid/fbthrift,SergeyMakarenko/fbthrift,sinjar666/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,sinjar666/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,Orvid/fbthrift,sinjar666/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,sinjar666/fbthrift,sinjar666/fbthrift,facebook/fbthrift,LinusU/fbthrift