URL matching fails with optional region and missing project name
**Describe the bug**
`taskcat test` fails with `FileNotFoundError [Errno 2] No such file or directory: '/home/villasv/projects/aws-airflow-stack/quickstart-turbine-airflow/templates/turbine-workerset.template'`

The correct path taskcat should be trying to access is `'/home/villasv/projects/aws-airflow-stack/templates/turbine-workerset.template'`

After digging up, I can see that there's an inconsistency with URLs when taskcat is reporting statuses for deeply nested stacks. At this section:
https://github.com/aws-quickstart/taskcat/blob/master/taskcat/_cfn/stack.py#L303-L308

For the `quickstart-aws-vpc` submodule, I get `url =  "https://tcat-quickstart-turbine-airflow-1vf1ri9d.s3.amazonaws.com/quickstart-turbine-airflow/submodules/quickstart-aws-vpc/templates/aws-vpc.template"` and `url_prefix() = "https://tcat-quickstart-turbine-airflow-1vf1ri9d.s3.us-east-1.amazonaws.com/quickstart-turbine-airflow"` (note the `us-east-1` extra).

But that doesn't yield an error. Later on, for one of the nested stacks, I get `url = "https://tcat-quickstart-turbine-airflow-1vf1ri9d.s3.amazonaws.com/quickstart-turbine-airflow/templates/turbine-workerset.template"` and `url_prefix() = "https://tcat-quickstart-turbine-airflow-1vf1ri9d.s3.amazonaws.com"` (note the missing project name).

**To Reproduce**
Happening on the develop branch of https://github.com/villasv/aws-airflow-stack

**Version (Please make sure you are running the latest version of taskcat)
 - Taskcat Version: latest master branch (00e3b916533d0cfcad8b43b101819401874fa9cb)

 Note: Python Version 3.6.5
diff --git a/taskcat/_cfn/template.py b/taskcat/_cfn/template.py
index 2f42671..5e0f0bd 100644
--- a/taskcat/_cfn/template.py
+++ b/taskcat/_cfn/template.py
@@ -1,4 +1,5 @@
 import logging
+import re
 from pathlib import Path
 from typing import Dict, List, Union
 
@@ -89,9 +90,12 @@ class Template:
     def url_prefix(self) -> str:
         if not self.url:
             return ""
+        regionless_url = re.sub(
+            r"\\.s3\\.(.*)\\.amazonaws\\.com", ".s3.amazonaws.com", self.url,
+        )
         suffix = str(self.template_path).replace(str(self.project_root), "")
         suffix_length = len(suffix.lstrip("/").split("/"))
-        url_prefix = "/".join(self.url.split("/")[0:-suffix_length])
+        url_prefix = "/".join(regionless_url.split("/")[0:-suffix_length])
         return url_prefix
 
     def _find_children(self) -> None:  # noqa: C901
['taskcat/_cfn/template.py']