Allow simple-smoke-test.sh to be run multiple times (#745)

`.github/scripts/simple-smoke-test.sh` creates and runs a container with
a default name (e.g. `hazelcast-oss`), but doesn't remove the container
afterwards, because later we query Docker for the logs.

This means when executed locally, subsequent invocations fail as the
container already exists.

Changed to remove the container if it already exists, before creation.

.github/scripts/simple-smoke-test.sh

@@ -6,6 +6,12 @@ set -o pipefail
 function test_docker_image() {
     local image=$1
     local container_name=$2
+
+    if [ "$(docker ps --all --quiet --filter name="$container_name")" ]; then
+      echo "Removing existing '$container_name' container"
+      docker container rm --force "$container_name"
+    fi
+
     echo "Starting container '$container_name' from image '$image'"
     docker run -it --name "$container_name" -e HZ_LICENSEKEY -e HZ_INSTANCETRACKING_FILENAME -d -p5701:5701 "$image"
     local key="some-key"