Refs #26822
AWS says to treat 503 errors, at least in the case of ec2 metadata
query, as backoff-retry (generally, we do _not_ retry on provider
level, but delegate this to higher levels). This patch adds special
treatment for 503:s (service unavailable) for both ec2 meta and
actual endpoint, doing exponential backoff.
Note: we do _not_ retry forever.
Not tested as such, since I don't get any errors when testing
(doh!). Should try to set up a mock ec2 meta with injected errors
maybe.
v2:
* Use utils::exponential_backoff_retry
(cherry picked from commit d22e0acf0b)
484e7aed2c