(QENG-967) Disable iptables on el hosts bringup.

Signed-off-by: Wayne <wayne@puppetlabs.com>
Ah, I misunderstood the name of that method--thought it was for general el related modifications. @anodelman how do you feel about calling it within the Beaker::Hypervisor.configure method? https://github.com/puppetlabs/beaker/blob/master/lib/beaker/hypervisor.rb#L81 I think you mentioned that this method is overridable in the JIRA ticket but disabling iptables on EL hosts seems like something that should be done regardless of hypervisor.