Switches to https://supermarket.getchef.com

This modifies knife cookbook site to use supermarket instead of
cookbooks.opscode.com. Additionally, it switches to using HTTPS instead
of HTTP.
Updates spec for supermarket
adding CHANGELOG for pr #1801
Use thread-safe OpenSSL::Digest instead of Digest
add CHANGELOG for pr #1807
Remove the bootstrap templates that does chef install via gems.
Deprecate --distro and --template-file options in favor of --template.
Remove encrypted_data_bag_secret distribution via Chef::Config and enable distributing it via knife[:secret] and knife[:secret_file].
Fixes based on the PR comments.
Specs for bootstrap cleanup.