fix(service): fixes importing private datasets in deployments with external gitlab

[Panaetius]

closes #3500

[mohammad-alisafaee]

LGTM, thank you!

[coveralls]

Pull Request Test Coverage Report for Build 5255484813

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 29 unchanged lines in 9 files lost coverage.
• Overall coverage increased (+1.1%) to 87.06%

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Files with Coverage Reduction	New Missed Lines	%
renku/core/dataset/providers/dataverse.py	1	88.86%
renku/infrastructure/repository.py	1	81.41%
renku/ui/cli/init.py	1	96.9%
renku/core/util/git.py	2	85.27%
renku/core/util/os.py	2	88.38%
renku/core/dataset/context.py	3	91.43%
renku/core/dataset/dataset.py	3	85.31%
renku/ui/service/controllers/api/mixins.py	3	78.79%
renku/ui/cli/service.py	13	62.69%

Totals
Change from base Build 5212908161:	1.1%
Covered Lines:	26152
Relevant Lines:	30039

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💛 - Coveralls