test: update test-run

Fixed formatting of reproduce files with recent pyyaml versions.

Background: test-run generates so called reproduce files in the
test/var/reproduce/ directory and accepts them as the argument of the
--reproduce option. It is convenient to share a reproducer for a problem
that appears when specific tests are run in a specific order.

tarantool/test-run#220
(cherry picked from commit a33cd1b)