update container clean up in unit & e2e tests

* changed calling syntax of xargs to avoid unhelpful error message
  when no signalboost_dispatcher containers exist

* remove changing directory preface in e2e test for parity with unit tests

bin/test/e2e

 #!/usr/bin/env bash
 
-pushd `pwd` # store current dir
-cd `dirname "$0"` # cd to script path
-cd ../../
-
 echo "----- running e2e tests..."
 docker-compose -f docker-compose-test-e2e.yml run test_runner
 
-
 echo "----- shutting down / cleaning up..."
 docker-compose -f docker-compose-test-e2e.yml down
-docker ps --filter name=signalboost_dispatcher* -aq | xargs docker rm -f
 
-popd # return to original dir
+docker ps --filter name=signalboost_dispatcher* -aq | xargs -I container_id docker rm -f container_id

bin/test/unit

@@ -10,3 +10,5 @@ docker-compose -f docker-compose-test-unit.yml run test_runner
 echo "--- spinning down environment..."
 
 docker-compose -f docker-compose-test-unit.yml down
+
+docker ps --filter name=signalboost_dispatcher* -aq | xargs -I container_id docker rm -f container_id