Fix OSError on _nc_dataset method

[vinisalazar]

Hi,

this is in relation to #261.

Summary of changes

• Call data.seek(0) after reading 'data' object for the first time (Closes #261)
• Update 'test_to_objects' to use gold standard Sensors server from #258
• Rewrite cassette

Thanks, V

[ocefpaf]

@vinisalazar in light of #272 do we still need this one?

[vinisalazar]

I don't think we do. Thanks!