working on #U4-3876
adds a unit test
adds another test for #U4-3876
Fixes: U4-3876 MySQL cmsContentXml Migration Error on 7.0.1 Upgrade
Merge remote-tracking branch 'origin/6.2.0' into 7.0.2

Conflicts:
	src/Umbraco.Core/Services/ContentService.cs
	src/Umbraco.Core/Services/MediaService.cs
	src/Umbraco.Tests/Persistence/Repositories/UserRepositoryTest.cs
fixed merge issues