This commit switches from git clone using ssh to git clone using https.

With SSH, the box must have ssh pub/priv keys for github private repos.
With HTTPS, we can reuse the GITHUB_ACCESS_TOKEN used for API calls.

It also changes the structure of the final file's key on S3 so that
the `/` characters cause folder-like behavior in S3 clients. And we
append a MD5 hash of the final tar.gz for validation.

On Heroku dynos we saw `resource unavailable errors` and 128 exit codes
for some clones.

I suspect that all 50 clones spinning up at nearly same millisecond is
causing resource issues.

This will help scale the activity on boxes with limited resources

The retry and backoff from prior commit was insufficient for ensuring
stable cloning behavior on Heroku dynos.

Heroku doesn't provide a persistent filestructure, so this commit
moves the mongo->s3 behavior into a streaming process that pipes
output from mongodump-> s3upload.

Conceptually it's `mongodump --stdout | s3upload`.

Files are overwriting each other on S3 when done hourly. Using
pseudo_uuid will fix it.