error in NDVI example

[juleshaas]

Issue in the NDVI example on the actinia website (https://actinia.mundialis.de/):

In the second step "polling the status URL it, until the status is 'finished':" does not work:

10:38 $ curl -u 'demouser:gu3st!pa55w0rd' \

-X GET
'https://actinia.mundialis.de/api/v1/resources/demouser/resource_id-87c6ddf2-0911-4e16-95eb-a4ea466f18ac'
{"message":"Resource does not exist","status":"error"}

Originally from #212
TODO: check if this is still relevant and fix