Switch to puppetlabs-ntp.

Updates our install_modules.sh file so that it uses
puppetlabs-ntp instead of kickstandproject-ntp. This provides
better multi distro NTP support.

Change-Id: I7b11e8c67a2e38653be281b5e6aa1d08768cc617
Reviewed-on: https://review.openstack.org/23204
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins
Update exim module to work on RHEL.

Parameterizes the exim module so that it can support multiple
distributions.

As part of this patch I also removed the explicit install
of exim4-base and exim4-config on Ubuntu. Just installing
exim4-daemon-light should be fine.

Change-Id: Ie09c5fa01509ebfadc92b8540f04181a2b13b667
Reviewed-on: https://review.openstack.org/23289
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins