[qa] change cutoff for extended tests to 10 minutes
[qa] change cutoff for extended tests to 10 minutes

Summary: As per title

Test Plan:
  ./test/functional/test_runner.py

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D1908

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