travis/gitlab/azure: Use bash to avoid a_test_which_does_not_exist

Bash allows for variables to expand only if non-empty:

	$ var=test
	$ echo ${var:+"$var"}
	test
	$ echo ${var:+"-k $var"}
	-k test
	$ var=
	$ echo ${var:+"-k $var"}

Use this feature to avoid the workaround.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

.gitlab-ci.yml

@@ -47,17 +47,14 @@ stages:
            --board ${TEST_PY_BD};
         exit $ret;
       fi
-    # "not a_test_which_does_not_exist" is a dummy -k parameter which will
-    # never prevent any test from running. That way, we can always pass
-    # "-k something" even when $TEST_PY_TEST_SPEC doesnt need a custom
-    # value.
     - virtualenv -p /usr/bin/python3 /tmp/venv
     - . /tmp/venv/bin/activate
     - pip install -r test/py/requirements.txt
+    # "${var:+"-k $var"}" expands to "" if $var is empty, "-k $var" if not
     - export PATH=/opt/qemu/bin:/tmp/uboot-test-hooks/bin:${PATH};
       export PYTHONPATH=/tmp/uboot-test-hooks/py/travis-ci;
       ./test/py/test.py --bd ${TEST_PY_BD} ${TEST_PY_ID}
-        -k "${TEST_PY_TEST_SPEC:-not a_test_which_does_not_exist}"
+        ${TEST_PY_TEST_SPEC:+"-k ${TEST_PY_TEST_SPEC}"}
         --build-dir "$UBOOT_TRAVIS_BUILD_DIR";
       ret=$?;
       if [[ $ret -ne 0 ]]; then