Traceback error related to identity endpoint in dcorch logs

Brief Description
-----------------
Traceback error messages are seen for identity endpoint in dcorch logs. These error messages have no effect on system behavior, but proper error handling must be done to avoid such traceback in logs.

Severity
--------
Minor

Steps to Reproduce
------------------
Add and manage a subcloud. Keep monitoring dcorch logs.

Expected Behavior
------------------
If any error/exception occurs, it must be properly handled.

Actual Behavior
----------------
Traceback error is seen in logs

Reproducibility
---------------
100% reproducible

System Configuration
--------------------
Distributed Cloud

Branch/Pull Time/Commit
-----------------------
Designer load built from a pull on March 28, 2020.

Last Pass
---------
Unknown

Timestamp/Logs
--------------
The screenshot of the dcorch logs is also given as an attachment for more readability.

Here is an example of the traceback:

2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity [-] Could not find role: df8a8e1e3536495fb762b72fa562ef0d. (HTTP 404) (Request-ID: req-b4ba8bc5-6ed8-4243-a063-14d5fddccbeb): NotFound: Could not find role: df8a8e1e3536495fb762b72fa562ef0d. (HTTP 404) (Request-ID: req-b4ba8bc5-6ed8-4243-a063-14d5fddccbeb)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity Traceback (most recent call last):
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/dcorch/engine/sync_services/identity.py", line 1517, in get_subcloud_resources
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity self.sc_ks_client)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/dcorch/engine/sync_services/identity.py", line 1103, in _get_resource_audit_handler
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity return self._get_assignments_resource(client)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/dcorch/engine/sync_services/identity.py", line 1226, in _get_assignments_resource
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity assignments = client.role_assignments.list()
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/keystoneclient/v3/role_assignments.py", line 124, in list
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity return super(RoleAssignmentManager, self).list(**query_params)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/keystoneclient/base.py", line 86, in func
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity return f(*args, **new_kwargs)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/keystoneclient/base.py", line 448, in list
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity list_resp = self._list(url_query, self.collection_key)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/keystoneclient/base.py", line 141, in _list
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity resp, body = self.client.get(url, **kwargs)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/keystoneauth1/adapter.py", line 375, in get
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity return self.request(url, 'GET', **kwargs)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/keystoneauth1/adapter.py", line 534, in request
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity resp = super(LegacyJsonAdapter, self).request(*args, **kwargs)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/keystoneauth1/adapter.py", line 237, in request
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity return self.session.request(url, method, **kwargs)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity File "/usr/lib/python2.7/site-packages/keystoneauth1/session.py", line 890, in request
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity raise exceptions.from_response(resp, method, url)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity NotFound: Could not find role: df8a8e1e3536495fb762b72fa562ef0d. (HTTP 404) (Request-ID: req-b4ba8bc5-6ed8-4243-a063-14d5fddccbeb)
2020-04-14 17:26:50.633 100684 ERROR dcorch.engine.sync_services.identity

Test Activity
-------------
Developer Testing

Workaround
----------
N/A