Comment 1 for bug 1657073

The error you're seeing there is harmless and unrelated to the problem you're seeing. To the extent that it's a problem at all (not really in this particular case), it'll be fixed by fixing bug 1626739.

Launchpad doesn't itself create signed assertions for the snaps it builds. Depending on your exact needs, you can either:

 * tell Launchpad to upload this snap to the edge channel in the store, after which you should be able to install it with "snap install --edge openhab";
 * generate a developer key using "snapcraft create-key" and "snapcraft register-key" if you haven't already done so, generate a signed snap-build assertion for the .snap file using "snapcraft sign-build", and add it to the system assertion database using "snap ack";
 * ignore the lack of signatures using "snap install --dangerous".