[Backport 4.1.x] SSRF Bypass to return internal host data

[afabiani]

Checklist

Reviewing is a process done by project maintainers, mostly on a volunteer basis. We try to keep the overhead as small as possible and appreciate if you help us to do so by completing the following items. Feel free to ask in a comment if you have troubles with any of them.

For all pull requests:

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• There is a ticket in https://github.com/GeoNode/geonode/issues describing the issue/improvement/feature (a notable exemption is, changes not visible to end-users)
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• Commit message must be in the form "[Fixes #<issue_number>] Title of the Issue"
• New unit tests have been added covering the changes, unless there is an explanation on why the tests are not necessary/implemented
• This PR passes all existing unit tests (test results will be reported by travis-ci after opening this PR)
• This PR passes the QA checks: black geonode && flake8 geonode
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Submitting the PR does not require you to check all items, but by the time it gets merged, they should be either satisfied or inapplicable.

[giohappy]

CircleCI is failing at bringing the Django container to a healthy state, but it's actually ok.
I've run the tests manually inside the CircleCI workspace and they passed, so we can merge.