Fix flaky user name uniqueness in specs
Fix flaky user name uniqueness in specs

Apparently Faker doesn't generate unique user names in a sequence of
calls and I sometimes get an uniquess violation error because of this.
This can be fixed by using FactoryGirl's sequence.

Tested:
- rspec

MarkUsProject/Markus,david-yz-liu/Markus,binuri/Markus,arkon/Markus,benjaminvialle/Markus,WilsonChiang/Markus,WilsonChiang/Markus,melneubert/Markus,jeremygoh/Markus,david-yz-liu/Markus,david-yz-liu/Markus,wkwan/Markus,ealonas/Markus,melneubert/Markus,ealonas/Markus,melneubert/Markus,jeremygoh/Markus,reidka/Markus,Lysette/Markus,SoftwareDev/Markus,reidka/Markus,wkwan/Markus,benjaminvialle/Markus,MarkUsProject/Markus,MarkUsProject/Markus,benjaminvialle/Markus,WilsonChiang/Markus,arkon/Markus,ealonas/Markus,WilsonChiang/Markus,reidka/Markus,finnergizer/Markus,ealonas/Markus,arkon/Markus,melneubert/Markus,reidka/Markus,ealonas/Markus,SoftwareDev/Markus,SoftwareDev/Markus,SoftwareDev/Markus,arkon/Markus,arkon/Markus,melneubert/Markus,ealonas/Markus,david-yz-liu/Markus,jeremygoh/Markus,binuri/Markus,finnergizer/Markus,david-yz-liu/Markus,jeremygoh/Markus,finnergizer/Markus,benjaminvialle/Markus,wkwan/Markus,melneubert/Markus,Lysette/Markus,SoftwareDev/Markus,MarkUsProject/Markus,jeremygoh/Markus,reidka/Markus,reidka/Markus,finnergizer/Markus,SoftwareDev/Markus,david-yz-liu/Markus,david-yz-liu/Markus,david-yz-liu/Markus,binuri/Markus,binuri/Markus,ealonas/Markus,MarkUsProject/Markus,finnergizer/Markus,binuri/Markus,arkon/Markus,Lysette/Markus,SoftwareDev/Markus,WilsonChiang/Markus,ealonas/Markus,benjaminvialle/Markus,jeremygoh/Markus,wkwan/Markus,Lysette/Markus,Lysette/Markus,WilsonChiang/Markus,jeremygoh/Markus,melneubert/Markus,benjaminvialle/Markus,reidka/Markus,finnergizer/Markus,Lysette/Markus,arkon/Markus,binuri/Markus,wkwan/Markus,wkwan/Markus,finnergizer/Markus,binuri/Markus,melneubert/Markus,MarkUsProject/Markus,WilsonChiang/Markus,arkon/Markus,jeremygoh/Markus,Lysette/Markus,benjaminvialle/Markus,finnergizer/Markus,MarkUsProject/Markus,melneubert/Markus,reidka/Markus,arkon/Markus,binuri/Markus,WilsonChiang/Markus,WilsonChiang/Markus,jeremygoh/Markus,wkwan/Markus,ealonas/Markus,david-yz-liu/Markus,binuri/Markus,MarkUsProject/Markus,reidka/Markus,finnergizer/Markus,wkwan/Markus,wkwan/Markus