Replacing bug with boo #950999.

Using ext4 for persistence will be temporary till btrfs is fixed, in the mean time this at least gets working live images.

Changing kiwi's default can't work as this change will have to be reverted when someone fixes btrfs. See boo #900922

May be reverting only hybridpersistent_filesystem="ext4" will be required when btrfs is fixed. The change to journald on live system is desirable any way.