Query Gerrit REST API https access using curl/wget tools

[chrisinmtown]

Extend the gerritstats downloader to query the REST API via HTTPS using curl or wget. This will allow use of this stats tool on gerrit repositories that block access to statistics by SSH but grant access via anonymous HTTPS.

Unfortunately the protocols are sharply different. The SSH access path is script friendly; the REST API is machine friendly. Both return JSON, but formatted significantly differently.

https://gerrit-review.googlesource.com/Documentation/rest-api.html