test: add flag to have Cucumber exit when tests are complete (#3252)

Description
---
Add the —exit flag to the Cucumber CI commands to force Cucumber to end when the tests are completed. This doesn’t solve the issue where something is keeping the Cucumber process running due to a poor shutdown though.

How Has This Been Tested?
---
N/A

.circleci/config.yml

@@ -122,14 +122,14 @@ commands:
           command: cargo build --release --bin tari_mining_node
       - run:
           name: Run cucumber scenarios
-          command: cd integration_tests && mkdir -p cucumber_output && node_modules/.bin/cucumber-js --tags "not @long-running and not @broken and not @flaky and not @wallet-ffi" --format json:cucumber_output/tests.cucumber
+          command: cd integration_tests && mkdir -p cucumber_output && node_modules/.bin/cucumber-js --tags "not @long-running and not @broken and not @flaky and not @wallet-ffi" --format json:cucumber_output/tests.cucumber --exit
       - run:
           name: Generate report
           command: cd integration_tests && node ./generate_report.js
           when: always
       - run:
           name: Run ffi cucumber scenarios
-          command: cd integration_tests && mkdir -p cucumber_output && node_modules/.bin/cucumber-js --tags "not @long-running and not @broken and not @flaky and @wallet-ffi" --format json:cucumber_output/tests-ffi.cucumber
+          command: cd integration_tests && mkdir -p cucumber_output && node_modules/.bin/cucumber-js --tags "not @long-running and not @broken and not @flaky and @wallet-ffi" --format json:cucumber_output/tests-ffi.cucumber --exit
       - run:
           name: Generate report (ffi)
           command: cd integration_tests && touch cucumber_output/tests-ffi.cucumber && node ./generate_report.js cucumber_output/tests-ffi.cucumber temp/reports/cucumber_ffi_report.html