Provide default value for ARTIFACTS variable if missing

This is required to prevent test script from failing if there's no
available location to write the videos captured during the browser e2e tests.

test/e2e-tests.sh

@@ -22,6 +22,7 @@ source $(dirname $0)/e2e-common.sh
 
 # Script entry point.
 
+ARTIFACTS="${ARTIFACTS:-`mktemp -d`}"
 SED="sed"
 START=1
 END=30
@@ -166,6 +167,7 @@ test_dashboard() {
   VIDEO_PATH=$ARTIFACTS/videos
   mkdir -p $VIDEO_PATH
   chmod -R 777 $VIDEO_PATH
+  echo "Videos of failing tests will be stored at $VIDEO_PATH"
   # In case of failure we'll upload videos of the failing tests
   # Our Cypress config will delete videos of passing tests before exiting
   docker run --rm --network=host -v $VIDEO_PATH:/home/node/cypress/videos dashboard-e2e || fail_test "Browser E2E tests failed"