libcgroup: fix QA warnings

fix the following warnings:
WARNING: For recipe libcgroup, the following files/directories were installed but not shipped in any package:
WARNING:   /lib/security/pam_cgroup.la
WARNING:   /lib/security/.debug
WARNING:   /lib/security/.debug/pam_cgroup.so.0.0.0
WARNING:   /lib/security/.debug/pam_cgroup.so
WARNING:   /lib/security/.debug/pam_cgroup.so.0

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>