access searchpath var as an instance var in erb template

Resolves this warning:

    Thu Oct 17 04:56:45 -0700 2013 Puppet (warning): Variable access via
    'searchpath' is deprecated. Use '@searchpath' instead.
    template[/etc/puppet/env/production/modules/resolv_conf/templates/resolv.conf.erb]:6
Merge pull request #11 from jhoblitt/erb_warnings

access searchpath var as an instance var in erb template