client: permute endpoints manually (for Go 1.9>)
client: permute endpoints manually (for Go 1.9>)

To keep backward compatibility, use old algorithm of
rand.Rand.Perm.

Reference: https://github.com/golang/go/commit/caae0917bff12751019cb4240e99874fa692e770#diff-d4a72c5ba8515eae95a093e0aec62635.

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

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