Fix libsss-sudo installation

On Debian, this is called libsss-sudo, not libsss_sudo. It is not
necessary to install it on other platforms anyway as they bundle it
with sssd or sssd-common.

Older versions of Debian and Ubuntu have libsss-sudo0 rather than
libsss-sudo. Despite the existence of this package, they annoyingly
forgot to build sudo with SSSD support. We'll install libsss-sudo0
anyway to prevent the recipe from breaking. Users may also wish to
roll their own sudo.
Stopping non-existent nscd breaks Debian

CentOS doesn't complain but Debian does for some reason. It is highly
unlikely that you would want both SSSD and NSCD on the same system
anyway so let's just remove it altogether.
Merge pull request #17 from yakara-ltd/debian_fixes

Debian fixes