fix(core): migrate Dockerfile after metadata

[Panaetius]

properly fixes migration issues.
Docker/Template migration is now done after metadata migration and double checks if the Dockerfile can be migrated.

[coveralls]

Pull Request Test Coverage Report for Build 7790158199

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A quick fix for this PR: rebase it; your next report should be accurate.

• -2 of 29 (93.1%) changed or added relevant lines in 3 files are covered.
• 5 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.01%) to 85.162%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
renku/core/migration/migrate.py	22	24	91.67%

Files with Coverage Reduction	New Missed Lines	%
renku/core/dataset/providers/dataverse.py	1	64.76%
renku/ui/cli/init.py	1	96.95%
renku/ui/cli/service.py	1	78.31%
renku/command/rollback.py	2	78.7%

Totals
Change from base Build 7787455799:	0.01%
Covered Lines:	26659
Relevant Lines:	31304

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💛 - Coveralls

[m-alisafaee]

LGTM. Thank you!