CBLT-179:  CURL_CMD="curl --fail --retry 10 --silent --show-error"

When curl is about to retry a transfer, it will first wait one second
and then for all forthcoming retries it will double the waiting time
until it reaches 10 minutes which then will be the delay between the
rest of the retries.

Change-Id: I90f5c8db7746a6f938487932acfc8e1e4084adec
Reviewed-on: http://review.couchbase.org/36532
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>