cleanup: fixes regex escape warnings in S3Uri.py, FileLists.py

Mark two strings in S3Uri.py and one string in FileLists.py as
literal regex strings to address "invalid escape sequence" syntax
warnings.

S3/FileLists.py

@@ -522,7 +522,7 @@ def _get_filelist_remote(remote_uri, recursive = True):
             uri_str = uri.uri()
             ## Wildcards used in remote URI?
             ## If yes we'll need a bucket listing...
-            wildcard_split_result = re.split("\*|\?", uri_str, maxsplit=1)
+            wildcard_split_result = re.split(r"\*|\?", uri_str, maxsplit=1)
 
             if len(wildcard_split_result) == 2:
                 ## If wildcards found

S3/S3Uri.py

@@ -119,7 +119,7 @@ def httpurl_to_s3uri(http_url):
 
         # Worst case scenario, we would like to be able to match something like
         # my.website.com.s3-fips.dualstack.us-west-1.amazonaws.com.cn
-        m = re.match("(.*\.)?s3(?:\-[^\.]*)?(?:\.dualstack)?(?:\.[^\.]*)?\.amazonaws\.com(?:\.cn)?$",
+        m = re.match(r"(.*\.)?s3(?:\-[^\.]*)?(?:\.dualstack)?(?:\.[^\.]*)?\.amazonaws\.com(?:\.cn)?$",
                      hostname, re.IGNORECASE | re.UNICODE)
         if not m:
             raise ValueError("Unable to parse URL: %s" % http_url)
@@ -167,7 +167,7 @@ def uri(self):
 
 class S3UriFile(S3Uri):
     type = "file"
-    _re = re.compile("^(\w+://)?(.*)", re.UNICODE)
+    _re = re.compile(r"^(\w+://)?(.*)", re.UNICODE)
     def __init__(self, string):
         match = self._re.match(string)
         groups = match.groups()