These commands outputs data that may not end with a newline. This
causes problems when the progress bar redraws, as that completely
wipes the last line of output. As nix key generate-secret outputs
a single line of text with no output, it shows up entirely blank,
making it look like nothing happened.
Fixes: lix-project/lix#320
Change-Id: I5ac706d71d839b6dfa760b60a351414cd96297cf