Extract the right distribution ID for mixed-capitalization distro names

Hi! In the PureOS Debian derivative with the switch to only relying on /etc/os-release, a few things broke because the distribution ID returned by lsb_release suddenly changed from "PureOS" to "Pureos". This patch uses the NAME property of os-release to work around the capitalization issue without breaking the existing usecases, restoring the previous behavior while still only relying on /etc/os-release.

Thanks for considering! Cheers, Matthias