Back compat for cycle point templating.

cylc-6 broke filename templating with ```cylc cycle-point --template``` for cylc-5 suites, which used ```YYYY```, ```MM```, ```DD``, and ```HH```.

Example on current master:
```
% cylc cyclepoint --template foo-YYYY-MM-DD-HH.nc 2014080812
foo-1414-08-08-HH.nc
```

And on this branch:
```
% cylc cyclepoint --template foo-YYYY-MM-DD-HH.nc 2014080812
foo-2014-08-08-12.nc
```