Add support for active luks mappings at populate time.
Add support for active luks mappings at populate time.

There will be no passphrase or key until/unless one is provided to
the luks format instance.

vpodzime/blivet,dwlehman/blivet,AdamWill/blivet,rvykydal/blivet,vpodzime/blivet,rhinstaller/blivet,AdamWill/blivet,rvykydal/blivet,dwlehman/blivet,vojtechtrefny/blivet,vojtechtrefny/blivet,rhinstaller/blivet,jkonecny12/blivet,jkonecny12/blivet