Retry failed uploads

[fkalis]

If there is a temporary problem with the internet connection when uploading many backup files, the upload of some files might fail.

If this happens it might be useful if the script waited for some seconds (e.g. 5 seconds) and retries the upload (up to 3 times).

[fkalis]

Let curl do the work: curl --retry 3 --retry-delay 5

From the manpage:

If a transient error is returned when curl tries to perform a transfer, it will retry this number of times before giving up. Setting the number to 0 makes curl do no retries (which is the default). Transient error means either: a timeout, an FTP 4xx response code or an HTTP 5xx response code.