fix: concurrent execuion completion logic

[vip-amzn]

Issue #, if available:

• Fix is_complete() logic:

The Issue with current logic:
For 5 tasks,

1. When tolerated_failure_count=2, but min_successful is NOT explicitly set, the code defaults min_successful to len(executables) (5 tasks)
2. With 3 successes and 2 failures (expected) (all 5 tasks completed), the completion check fails:
   • tolerated_failure_count is None → False (we have tolerance set)
   • failure_count == 0 → False (we have 2 failures)
   • success_count >= min_successful → 3 >= 5 → False ❌
3. Result: is_complete() returned False even though all tasks were done, causing an infinite wait

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