Autojoin cluster during Kong.init() with external process supervisor

Merge remote-tracking branch 'Mashape/master' into external-supervisor

Removing print message

release: 0.5.4

[hotfix/galileo] path fix

fix(cli) re-enable search in $PATH for nginx executable

Since IO.file_exists was being called and of course returned false when
called with just `nginx`, the command was never executed, and no chance
was given to the shell to try to find the executable in the $PATH.

Fix Kong#610

Merge pull request Kong#619 from Mashape/docs/changelog

[docs/changelog] 0.5.1 changes

Adding missing statement for Kong#571

Changelog SSL default dir

Former-commit-id: ecaeb5dc15b5668dac49934e9fc543ae11c73630

adding buffer.lua to rockspec

Former-commit-id: a09c2721bd17996a081fa546df5d712bba226113