I couldn't succeed using certbot on raspbian jessie. I tried both installing it (and its dependency) from raspbian testing (deb http://mirrordirector.raspbian.org/raspbian/ testing main) and from debian arm jessie-backports (deb http://ftp.fr.debian.org/debian/ jessie-backports main).
All my tries resulted in an error-less installation, but certbot itself issues a "Illegal instruction" wathever the argument givent (or even with no argument at all).
I saw there were many problem around this, but I couldn't find any correct answer around it yet. It is, lot of people think, bind to the RPi architecture armv6 when debian arm uses armv7 ? - this would explains the fail for je jessie-backport. What about the raspbian testing issue, then ?
My actual testing ground is a RPi rev1B. I'm up to try stuffs if you have clues !