Merge branch 'jjardon/ci_show_timings-bst-1.2' into 'bst-1.2'

[bst-1.2] .gitlab-ci.yml: Show timing of the 20 slowest tests

See merge request BuildStream/buildstream!728
diff --git a/setup.cfg b/setup.cfg
index 173917c..159c665 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -11,7 +11,7 @@
 test=pytest
 
 [tool:pytest]
-addopts = --verbose --basetemp ./tmp --pep8 --pylint --pylint-rcfile=.pylintrc --cov=buildstream --cov-config .coveragerc
+addopts = --verbose --basetemp ./tmp --pep8 --pylint --pylint-rcfile=.pylintrc --cov=buildstream --cov-config .coveragerc --durations=20
 norecursedirs = integration-cache tmp __pycache__ .eggs
 python_files = tests/*/*.py
 pep8maxlinelength = 119