Use slower delays for smoke test throttle errors

[jamesls]

In the case of a throttle error we want to slow down our
request sending rate moreso than exponential backoff. This
commit adds a fixed 10 second minimum delay along with exponential
backoff of 2 ^ retry_attempt seconds.

Verified I could see log messages and expected delays when running these tests in a loop:

tests.integration.test_smoke: DEBUG: Using custom retry delay of: 11

[codecov-io]

Codecov Report

Merging #1882 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #1882   +/-   ##
========================================
  Coverage    92.56%   92.56%           
========================================
  Files           53       53           
  Lines        10001    10001           
========================================
  Hits          9257     9257           
  Misses         744      744

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