import openapi: fix when missing operation id in spec

[eguzki]

in OAS 2.0, when there is no operation_id attribute, i.e.

....
"paths": {
    "/products": {
      "get": {
        "summary": "Product Types",
        "description": "The Products endpoint returns information about the Uber products offered at a given location. The response includes the display name and other details about each product, and lists the products in the proper display order.",
        "parameters": [
          {
            "name": "latitude",
            "in": "query",
            "description": "Latitude component of location.",
            "required": true,
            "type": "number",
            "format": "double"
          },
          {
            "name": "longitude",
            "in": "query",
            "description": "Longitude component of location.",
            "required": true,
            "type": "number",
            "format": "double"
          }
        ],
        "tags": [
          "Products"
        ],
        "responses": {
          "200": {
            "description": "An array of products",
            "schema": {
              "type": "array",
              "items": {
                "$ref": "#/definitions/Product"
              }
            }
          },
          "default": {
            "description": "Unexpected error",
            "schema": {
              "$ref": "#/definitions/Error"
            }
          }
        }
      }
    }
....

method names are computed:

"#{operation[:verb]}#{operation[:path].tr('/{}', '')}"