Update nautilus driver to accommodate new version of nautilus

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Nautilus has been updated to version 9.3 and the following updates need to be made to the nautilus driver in the ehb-datasources

• Nautilus-REST has been upgraded to Django 1.10. Django will ignore any heading item with an underscore, so the heading containing the credentials of the user needs to change from NAUTILUS_CREDS to NAUTILUS-CREDS. The unit tests also need to be updated to accommodate this change.

• Nautilus-REST has changed rest libraries moving to django rest framework from restlib. The nautilus driver needs to be changed to force evaluation of the status code to a string.

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Dev commits:

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