Add default to read_deleted in context's from_dict

this is follow-up to Ic94323658c89df1c1ff32f511ca23502317d0f00

currently the defaults in __init__ and from_dict of RequestContext
for read_deleted property are different:
- in __init__ it is 'no'
- in from_dict, it is effectively None.
And at the same time, this property is not allowed to be None.

As a result, the new _sanitize_context in oslo.messaging can not create
a sanitized context copy with error

read_deleted can only be one of 'no', 'yes' or 'only', not None

Related-Bug: #2030976
Change-Id: Ifb660688c590fb1c32cbe0ae03e0ea444f19cbb8

manila/context.py

@@ -106,7 +106,7 @@ class RequestContext(context.RequestContext):
             project_id=values.get('project_id'),
             project_name=values.get('project_name'),
             domain_id=values.get('domain_id'),
-            read_deleted=values.get('read_deleted'),
+            read_deleted=values.get('read_deleted', 'no'),
             remote_address=values.get('remote_address'),
             timestamp=values.get('timestamp'),
             quota_class=values.get('quota_class'),