Don't include the pgdg recipes on the wrong machine types

Don't bother including enable_pgdg_apt on rhel, and don't include
enable_pgdg_yum on Debian.
Update repo key location
Merge pull request #180 from bai-cookbooks/update-key

Update repo key location
CentOS 7 support
Add missing dir /etc/sysconfig/pgsl that's missing when using centos 7
Merge pull request #178 from schrodinger/pgdg_ubuntu

Don't include the pgdg recipes on the wrong machine types
Merge pull request #182 from stephenlauck/sysconfig_dir_centos_70

Add missing dir /etc/sysconfig/pgsl that's missing when using centos 7
Merge pull request #183 from webvit/platforms

CentOS 7 support
posgresql cookbook version 3.6.6
Merge pull request #184 from hw-cookbooks/develop

Release 3.6.6