Simplify error message if geoprocessing down
Simplify error message if geoprocessing down

In case the geoprocessing service is unreachable, we now
show this simplified message, instead of exposing inner
details to the user.

Without this, the error message would be something like:

[analyze_nlcd] HTTPConnectionPool(host='localhost', port=8090): Max retries exceeded with url: /run (Caused by NewConnectionError('<requests.packages.urllib3.connection.HTTPConnection object at 0x7fa3895a0a50>: Failed to establish a new connection: [Errno 111] Connection refused',))

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