Restarting stuck downloads

[MattBlissett]

When a download is stuck for some reason (see other issues), we need a way to rerun it.

This code prevents the status being updated to SUCCEEDED:

occurrence/occurrence-download-service/src/main/java/org/gbif/occurrence/download/service/DownloadRequestServiceImpl.java

Lines 274 to 283 in 17de665

	if (Download.Status.SUCCEEDED.equals(download.getStatus())
	|| Download.Status.FAILED.equals(download.getStatus())
	|| Download.Status.KILLED.equals(download.getStatus())) {
	// Download has already completed, so perhaps callbacks in rapid succession have been
	// processed out-of-order
	LOG.warn(
	"Download {} has finished, but Oozie has sent a RUNNING callback. Ignoring it.",
	downloadId);
	return;
	}

And the recent changes to remove the DOI prevent a DOI from being assigned.

An admin API method to restart a failed download would be useful.