alternator-test: limit the number of retries to 3
alternator-test: limit the number of retries to 3

In order to decrease the developer's time spent on waiting
for boto3 to retry the request many times, the retry count
is configured to be 3.
Two major benefits:
 - vastly decrease wait time when debugging a failing test
 - for requests which are expected to fail, but return results
   not compatible with boto3, execution time is decreased

Tests: alternator-test(local,remote)

Message-Id: <a6cc00f4e1c10a3b74e0bb523f2beeca92a45c9e@scylladb.com>

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