bionic-amd64-tf-a-build: Use exponential backoff in curl operations

According to man curl:
"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.  By using --retry-delay
you  disable  this  exponential  backoff  algorithm."

So, we should not use explicit --retry-delay, and instead should
drop it and rely on exponential backoff delay, which should make
retries more robust.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I33741a626f69ea8effb4820707acd418be5bd73e
1 file changed