Inline NamespaceStorageSupport.accessNamespaces()

We have multiple callers, but all of duplicate the functionality
of getLocalNamespace(). Inline accessNamespaces() into
getLocalNamespace() and adjust users to use that instead duplicating its
code.

This removes a the need for a number of warning suppressions and makes
it clearer as to what is going on.

Change-Id: Ia210c6275b64093063eaf58a67412e94c3a29419
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>