clientv3/integration: fix license, minor nits in leasing_test.go
clientv3/integration: fix license, minor nits in leasing_test.go

Signed-off-by: Gyu-Ho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

visheshnp/etcd,fanminshi/etcd,rnaveiras/etcd,coreos/etcd,xiang90/etcd,ajityagaty/etcd,glevand/coreos--etcd,YuleiXiao/etcd,etcd-io/etcd,rnaveiras/etcd,akauppi/etcd,vimalk78/etcd,sebrandon1/etcd,mqliang/etcd,sebrandon1/etcd,dannysauer/etcd,glevand/coreos--etcd,mqliang/etcd,heyitsanthony/etcd,mkumatag/etcd,li-ang/etcd,mkumatag/etcd,bluebreezecf/etcd,mkumatag/etcd,joshix/etcd,rnaveiras/etcd,dannysauer/etcd,bluebreezecf/etcd,visheshnp/etcd,YuleiXiao/etcd,lorneli/etcd,sinsharat/etcd,whuwxl/etcd,lorneli/etcd,coreos/etcd,gyuho/etcd,etcd-io/etcd,joshix/etcd,ajityagaty/etcd,li-ang/etcd,cockroachdb/etcd,heyitsanthony/etcd,fanminshi/etcd,sinsharat/etcd,ajityagaty/etcd,bdarnell/etcd,bdarnell/etcd,mqliang/etcd,vimalk78/etcd,cockroachdb/etcd,xiang90/etcd,etcd-io/etcd,gyuho/etcd,akauppi/etcd,whuwxl/etcd