Code review comment for ~litios/ubuntu-security-tools:feature/esm-schroot

Hi David,

Thanks for the MP and for saving keystrokes in the future!
One minor issue on my end, I set up my ESM schroots manually following the wiki (https://wiki.ubuntu.com/SecurityTeam/BuildEnvironment#Setting_up_a_chroot_for_Extended_Security_Maintenance), and the names go like `esm-bionic-amd64`. They were put together with all hyphens, and no separation for `-infra` and `-apps`. Not sure if we should support this naming scheme though; I'm happy to continue to use `-c esm-$rel-amd64`.