Throw exception when consecutive slashes detected in URL path

S3 can tolerate consecutive slash in object key, such as "path//object"
but S3 will treat it different to "path/object".

User misconfiguration may result in excessive use of S3 storage space.
So detect and throw exception if consecutive slashes is detected in URL
path.

rpm_s3_mirror/repository.py

@@ -144,6 +144,8 @@ def __init__(self, base_url: str):
             base_url += "/"
         self.base_url = base_url
         self.path = urlparse(base_url).path
+        if self.path.find("//") != -1:
+            raise ValueError("Consecutive slashes detected in URL path")
         self.session = get_requests_session()
 
     def has_updates(self, since: datetime) -> bool: