Restoring encrypted DB to SQL vNext
You might be running into a bug in how SQL Server vNext CTP1.2 handles filepaths. To CREATE CERTIFICATE from a backup, you currently need to pre-pend a 'c:' and use backslashes ('\') instead of forward slashes. This will be fixed soon :)

Here's a demo for the scenario you're trying to do (backup an encrypted database and restore it on a SQL vNext on Linux instance). Let me know if it clarifies things for you.

https://github.com/tmullaney/tde-migration-demo