Set SSL_CERT_FILE environment variable on windows when it's not set

1. Set SSL_CERT_FILE environment variable on windows when it's not set during `require 'openssl'`
1. Bump embedded Chef Client app to 11.16.0 (resolves Mac 10.8 test failures in CI)
1. Fixes https://github.com/opscode/chef-dk/issues/106
1. Fixes 3rd checkbox at https://github.com/opscode/chef/issues/1542

/cc: @opscode/client-engineers, @schisamo 
We could open the file with "a" for append mode.