Allow re-runs of qmin system test

The qmin test is inherently unstable. It fails quite often with failure
modes described in GL #904. Allow the pytest runner to re-run the test
up to 3 times to only detect a more persistent and reproducible failures
rather than random noise caused by the nature of the test.

bin/tests/system/qmin/tests_sh_qmin.py

@@ -9,6 +9,10 @@
 # See the COPYRIGHT file distributed with this work for additional
 # information regarding copyright ownership.
 
+import pytest_custom_markers
 
+
+# The qmin test is inherently unstable, see GL #904 for details.
+@pytest_custom_markers.flaky(max_runs=3)
 def test_qmin(run_tests_sh):
     run_tests_sh()