shim_util issue in translating "CLOUDSDK_API_ENDPOINT_OVERRIDES_STORAGE" parameter from .boto config

[brahma19]

.boto has entry for
[Credentials]
gs_json_host = foo.bar
[GSUtil]
use_gcloud_storage=True

running the gsutil command fails with below error:
ERROR: (gcloud.storage.ls) Invalid value for property [api_endpoint_overrides/storage]: The endpoint_overrides property must be an absolute URI beginning with http:// or https:// and ending with a trailing '/'.

PFB the debug log
DEBUG: (gcloud.storage.ls) Invalid value for property [api_endpoint_overrides/storage]: The endpoint_overrides property must be an absolute URI beginning with http:// or https:// and ending with a trailing '/'. [https://foo.bar/storage/v1] is not a valid endpoint override. Traceback (most recent call last): File "/apps/opt/application/google-cloud-sdk/lib/googlecloudsdk/core/properties.py", line 4147, in Validate self.__validator(value) File "/apps/opt/application/google-cloud-sdk/lib/googlecloudsdk/core/properties.py", line 1425, in EndpointValidator raise InvalidValueError( googlecloudsdk.core.properties.InvalidValueError: The endpoint_overrides property must be an absolute URI beginning with http:// or https:// and ending with a trailing '/'. [https://foo.bar//storage/v1] is not a valid endpoint override.

To Fix:
Need to add trailing "/" in the shim_util when returning the translated value
https://github.com/GoogleCloudPlatform/gsutil/blob/master/gslib/utils/shim_util.py#L278