Issue title: enable-puppetlabs-pc1-repo not honored on CentOS 7.3 install
 Issue body: When I set enable-puppetlabs-pc1-repo: 'true' (which is no boolean but works on Fedora installs) to a CentOS 7.3 install the repo is not added and there is still the Puppet 3.6.x version on CentOS 7.3

Is this a bug or what do I do wrong ?
 Comments: 
 Comment 0: It seems that this is ignored from my finish preview:

rpm -Uvh https://yum.puppetlabs.com/puppetlabs-release-pc1-el-7.noarch.rpm




if [ -f /usr/bin/dnf ]; then
  dnf -y install puppet-agent
else
  yum -t -y install puppet-agent
fi
 Comment 1: Is your template exactly like in our repo is it different?
 Comment 2: It's a copy/paste from your repo.

2017-03-08 8:57 GMT+01:00 Ewoud Kohl van Wijngaarden <
mthompson@example.org>:

> Is your template exactly like in our repo is it different?
>
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> You are receiving this because you authored the thread.
> Reply to this email directly, view it on GitHub
> <https://github.com/theforeman/community-templates/issues/368#issuecomment-284972545>,
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 Comment 3: This seems to be solved on he latest template from 1 march. Thanks for updating this ticket ;)
{'source': 'GithubIssues', 'repo_name_with_owner': 'theforeman/community-templates', 'issue_id': 210154812, 'repo_stars': 141.0}