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 pull request #117 from UV-CDAT/createVariable-wrong-axes-tuple

Issue 182 "Improve handling of 'axes=' parameter of cdms2.createVariable"