Handle verify_api_cert parameter by copying trusted certificate file to ...

Handle verify_api_cert parameter by copying trusted certificate file to client before client.rb is updated

Trusted certificates and verify_api_cert is handled with knife bootstrap command during initial bootstrap but for existing clients, this change will copy trusted certificate of Chef server from URI in node['chef_client']['trusted_cert'] to /etc/chef/trusted_certs directory if 
- verify_api_cert attribute is set to true and 
- node['chef_client']['trusted_cert'] attribute is not empty

If verify_api_cert is true and 'trusted_cert' attribute is not set, then in order not to break SSL communication, code will set verify_api_cert to false for that chef-client session.