wal: Use known dir-path in log message
wal: Use known dir-path in log message

Signed-off-by: Ted Yu <22f3e725b314afeca4d45e12683c560674029d21@gmail.com>

li-ang/etcd,etcd-io/etcd,rnaveiras/etcd,cockroachdb/etcd,dannysauer/etcd,mkumatag/etcd,ajityagaty/etcd,mqliang/etcd,coreos/etcd,gyuho/etcd,etcd-io/etcd,dannysauer/etcd,coreos/etcd,mqliang/etcd,mqliang/etcd,mkumatag/etcd,cockroachdb/etcd,rnaveiras/etcd,mkumatag/etcd,ajityagaty/etcd,li-ang/etcd,rnaveiras/etcd,etcd-io/etcd,ajityagaty/etcd,gyuho/etcd