use concatfragments.rb on AIX

AIX find does not support the print0 option. It's basically the same as on Solaris:

Debug: Executing '/var/lib/puppet/concat/bin/concatfragments.sh -o "/var/lib/puppet/concat/_var_ossec_etc_ossec-agent.conf/fragments.concat.out" -d "/var/lib/puppet/concat/_var_ossec_etc_ossec-agent.conf" -t'
Debug: /Stage[main]/Ossec::Client/Concat[/var/ossec/etc/ossec-agent.conf]/Exec[concat_/var/ossec/etc/ossec-agent.conf]/unless: find: bad option -print0