Debian: Fix ugly error deleting a patch strategy

A JSONDecodeError is raised when deleting a patch strategy
that exists. (the error is not seen if no strategy exists)

sw-manager patch-strategy delete
Expecting value: line 1 column 1 (char 0)

The issue is the JSON decoder does not handle an empty
string. The empty string is a byte string on debian which
runs on python3 so the comparison check needed to be
updated.

Test Plan:
  Verify that a patch strategy can be deleted on Debian
without ugly messages.
  Verify that a non existant patch strategy can be deleted
on Debian without ugly messages.

Partial-Bug: 1974475
Signed-off-by: Al Bailey <al.bailey@windriver.com>
Change-Id: I18f84e20abf43a342e996c4752654bad3261e5a6

nfv/nfv-client/nfv_client/openstack/rest_api.py

@@ -45,7 +45,9 @@ def request(token_id, method, api_cmd, api_cmd_headers=None,
 
         response_raw = url_request.read()
 
-        if response_raw == "":
+        # python2 the reponse may be an empty string
+        # python3 the response may be an empty byte string
+        if response_raw == "" or response_raw == b"":
             response = dict()
         else:
             response = json.loads(response_raw)