[Merge] ~jibel/ubuntu-release-upgrader:fix_deb2snap_lp1856862 into ubuntu-release-upgrader:ubuntu/master

[Jean-Baptiste Lallement]

I tested and the tests passed. Although I didn't try with autopkgtest. I'll do that.
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https://code.launchpad.net/~jibel/ubuntu-release-upgrader/+git/ubuntu-release-upgrader/+merge/376999
Your team Ubuntu Core Development Team is requested to review the proposed merge of ~jibel/ubuntu-release-upgrader:fix_deb2snap_lp1856862 into ubuntu-release-upgrader:ubuntu/master.