Handles cdms2.createVariable() with non-tuple axes

If a single value is passed as the axes parameter (for instance, because
we forgot the trailing comma), a one-element tuple is assumed.
Accepts all iterable of axes, not just tuple&list
Merge remote-tracking branch 'devel/createVariable-wrong-axes-tuple'

* devel/createVariable-wrong-axes-tuple:
  Accepts all iterable of axes, not just tuple&list
  Handles cdms2.createVariable() with non-tuple axes