Fix elastic agent startup after SSL support removed

  - use a more modern fallback agent version that will not verify
    the presence of the `Cruise-Server-Ssl-Port` header
  - update to OpenJDK 13

gocd#7 - Create config dir before writing to autoregister.properties …

…file.

Ignore NSG ID if it is empty

Fix wrong plugin ID key

Merge pull request gocd#4 from arvindsv/update-docs

Update documentation

Upgrade gradle, rubygems

Showcase all internal linking on the readme itself

Showcase all internal linking on the readme itself

Merge pull request gocd#2 from maheshp/doc_changes

Re-organizing the docs

Initial Commit

* Initial commit with changes from private repo till
  revision -  e80111761c191ee6366a2af830fa53e1e092fd95