Remove nullable=True because it is set by default in db
Remove nullable=True because it is set by default in db

Change-Id: I5d01658926e5cb02f9c5be529df7917a349ba49d
Signed-off-by: Shane Wang <5003ec19d9bcd185a108cc3aad1a79fb91ee061c@intel.com>

aplanas/rally,aforalee/RRally,paboldin/rally,paboldin/rally,gluke77/rally,pandeyop/rally,gluke77/rally,openstack/rally,varunarya10/rally,eayunstack/rally,shdowofdeath/rally,yeming233/rally,vefimova/rally,pandeyop/rally,eayunstack/rally,ytsarev/rally,go-bears/rally,redhat-openstack/rally,openstack/rally,amit0701/rally,openstack/rally,vponomaryov/rally,vganapath/rally,afaheem88/rally,amit0701/rally,pyKun/rally,group-policy/rally,aforalee/RRally,cernops/rally,shdowofdeath/rally,vganapath/rally,yeming233/rally,ytsarev/rally,gluke77/rally,vganapath/rally,amit0701/rally,group-policy/rally,paboldin/rally,gluke77/rally,openstack/rally,vefimova/rally,go-bears/rally,afaheem88/rally,pyKun/rally,eonpatapon/rally,vganapath/rally,eonpatapon/rally,group-policy/rally,redhat-openstack/rally,aplanas/rally,varunarya10/rally,eayunstack/rally,cernops/rally,vponomaryov/rally