Configure puppet.conf on RHEL.

Fixes an issue where puppet.conf was only getting created
on Ubuntu machines. We actually need this file on *all* slaves.

Change-Id: I2d9810acd1e834853b00a9ebd1f0a1e5406a6ca9
Reviewed-on: https://review.openstack.org/23573
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins
Pin puppet version via puppetlabs.repo on RHEL.

Updates our install_puppet.sh script so that we pin the puppet
version on RHEL.

In doing this I dropped the explicit puppet version used on
the 'yum install' command since it is no longer required.

Here doc is quoted to avoid variable expansion.

Change-Id: I5e45182b67fe9533b92d1132fef6888fdd5d96b1
Reviewed-on: https://review.openstack.org/23574
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins