Trivial: Fix docs for functions

This patch fixes some comments in code:
 - Now suffixes can be string in _merge_candidates()
 - Remove old doc for `allow_forbidden` parameter in
   RequestGroup.dict_from_request
 - Delete unnecessary space in ResourceClassCache

Change-Id: I6ffc19eea84b45dd452bc61d2a2007b6572719ad

placement/lib.py

@@ -197,8 +197,7 @@ class RequestGroup(object):
         If a trait in the required parameter is prefixed with ``!`` this
         indicates that that trait must not be present on the resource
         providers in the group. That is, the trait is forbidden. Forbidden
-        traits are only processed  if ``allow_forbidden`` is True. This allows
-        the caller to control processing based on microversion handling.
+        traits are processed only if the microversion supports.
 
         The return is a dict, keyed by the suffix of these RequestGroup
         instances (or the empty string for the unidentified group).

placement/objects/allocation_candidate.py

@@ -735,7 +735,7 @@ def _merge_candidates(candidates, rw_ctx):
     For that merged list of alloc_reqs, a corresponding provider_summaries is
     produced.
 
-    :param candidates: A dict, keyed by integer suffix or '', of tuples of
+    :param candidates: A dict, keyed by suffix string or '', of tuples of
             (allocation_requests, provider_summaries) to be merged.
     :param rw_ctx: RequestWideSearchContext.
     :return: A tuple of (allocation_requests, provider_summaries).

placement/resource_class_cache.py

@@ -52,7 +52,7 @@ def _refresh_from_db(ctx, cache):
 
 
 class ResourceClassCache(object):
-    """A  cache of integer and string lookup values for resource classes."""
+    """A cache of integer and string lookup values for resource classes."""
 
     def __init__(self, ctx):
         """Initialize the cache of resource class identifiers.