Treat RHEL 7 and later like Fedora w/r/t iptables

RHEL 7 replaces legacy init with systemd, and must be treated like
Fedora w/r/t iptables persistence.  This patches checks
operatingsystemrelease in addition to operatingsystem in order
to differentiate between RHEL 7 and earlier releases.

Both RHEL 7 and recent Fedora releases require the iptables-services
package to support the commands in lib/puppet/util/firewall.rb.

This also corrects the path to /usr/libexec/iptables/iptables.init.
correct spelling of "&&" to "and"
fix errors noted by travis-ci

I like explicitly quoted strings, but apparently Travis doesn't.
Update firewall.rb

SNAT: typo in error message when tosource parameter is missing.
In lib/puppet/provider/firewall/iptables.rb we test on boolean flags when building iptables args:

        # If socket is true then do not add the value as -m socket is standalone
        if known_booleans.include?(res) then
          if resource[res] == :true then
            resource_value = nil
          else
            # If the property is not :true then we don't want to add the value
            # to the args list
            next
          end
        end

This evaluates to false on the reap flag in a definition like this:
    firewall { '001 rate limit ssh attempts':
        port   => [22],
        proto  => tcp,
        tcp_flags => "FIN,SYN,RST,ACK SYN",
        recent => 'rcheck',
        rsource => true,
        rname => 'ssh-syn4',
        rseconds => 30,
        rhitcount => 3,
        reap => true,
        jump => drop,
    }

This is because the value is not defined as a string, so the reap flag is not added to the args. This patch defines reap as a string true or false to match others like rsource.
Merge pull request #340 from simon-martin/master

--reap flag is not added to iptables command
Merge pull request #339 from cure/master

Fix typo in SNAT error message
Merge pull request #338 from larsks/master

Treat RHEL 7 and later like Fedora w/r/t iptables
Fix failing persist_iptables test on RHEL7 and Fedora
spec: Use appropriate operatingsystemrelease for RedHat/CentOS/Fedora
Merge pull request #341 from jeckersb/rhel7-spec-fix

Fix failing persist_iptables test on RHEL7 and Fedora
Apply firewall resources alphabetically
(doc) Sync latest CONTRIBUTING.md

This is the latest CONTRIBUTING.md from
https://github.com/puppetlabs/puppet/blob/master/CONTRIBUTING.md

The old version has out of date links.
(doc) Update links for modules

For modules, the JIRA project is MODULES not PUP.
Link to the module contributing guide, instead of core puppet
(doc) Update link to JIRA

Issue tracking has been moved from github to JIRA.
(MODULES-689) Add support for connlimit and connmark
(MODULES-689) connlimit and connmark acceptance tests
Merge pull request #344 from csschwe/add_connection_limit

(MODULES-689) Add support for connlimit and connmark
Update README
Fix support for Fedora Rawhide

On Fedora facter $::operatingsystemrelease can be integer version of Fedora or string Rawhide.