fixes #2121, #2069 - restrict importers and ENC to puppetmasters and users

CVE-2013-0171: report and fact importers parse YAML directly from the remote
host without authentication. Untrusted YAML can instantiate objects and be
used to exploit Foreman.

CVE-2013-0174: external nodes (ENC) output is available to any source and
could contain sensitive information, e.g. root password.

The restrict_registered_puppetmasters setting (default: on) now only permits
access to the three routes if the remote host has a smart proxy registered
with the Puppet feature.

The require_ssl_puppetmasters setting (default: on) requires a client SSL
certificate on HTTPS requests. The CN is checked against known smart proxies
as above. :require_ssl in settings.yaml is recommended to disable HTTP.

Ensure ENC (node.rb) and report (foreman.rb) scripts are updated to supply
client SSL certificates.