Add the ability to run dgoss when the docker daemon is not local. (#271)

* Add the ability to run dgoss when the docker daemon is not local

* Fix a typo

extras/dgoss/README.md

@@ -91,3 +91,7 @@ docker container when writing tests (i.e. `dgoss edit`). If set, the
 `--vars` flag is passed to `goss validate` commands inside the container.
 If unset (or empty), the `--vars` flag is omitted, which is the normal behavior.
 (Default: `''`).
+
+##### GOSS_FILES_STRATEGY
+Strategy used for copying goss files into the docker container. If set to `'mount'` a volume with goss files is mounted and log output is streamed into the container as `/goss/docker_output.log` file. Other strategy is `'cp'` which uses `'docker cp'` command to copy goss files into docker container. With the `'cp'` strategy you lose the ability to write tests or waits against the docker output. The `'cp'` strategy is required especially when docker daemon is not on the local machine. 
+(Default `'mount'`)

extras/dgoss/dgoss

@@ -25,9 +25,26 @@ run(){
     [[ -e "${GOSS_FILES_PATH}/goss.yaml" ]] && cp "${GOSS_FILES_PATH}/goss.yaml" "$tmp_dir"
     [[ -e "${GOSS_FILES_PATH}/goss_wait.yaml" ]] && cp "${GOSS_FILES_PATH}/goss_wait.yaml" "$tmp_dir"
     [[ ! -z "${GOSS_VARS}" ]] && [[ -e "${GOSS_FILES_PATH}/${GOSS_VARS}" ]] && cp "${GOSS_FILES_PATH}/${GOSS_VARS}" "$tmp_dir"
-    info "Starting docker container"
-    id=$(docker run -d -v "$tmp_dir:/goss" "${@:2}")
-    docker logs -f "$id" > "$tmp_dir/docker_output.log" 2>&1 &
+
+    # Switch between mount or cp files strategy
+    GOSS_FILES_STRATEGY=${GOSS_FILES_STRATEGY:="mount"}
+    case "$GOSS_FILES_STRATEGY" in
+      mount)
+        info "Starting docker container"
+        id=$(docker run -d -v "$tmp_dir:/goss" "${@:2}")
+        docker logs -f "$id" > "$tmp_dir/docker_output.log" 2>&1 &
+        ;;
+      cp)
+        info "Creating docker container"
+        id=$(docker create "${@:2}")
+        info "Copy goss files into container"
+        docker cp $tmp_dir $id:/goss
+        info "Starting docker container"
+        docker start $id > /dev/null
+        ;;
+      *) error "Wrong goss files strategy used! Correct options are \"mount\" or \"cp\"."
+    esac
+
     log_pid=$!
     info "Container ID: ${id:0:8}"
 }