DISPATCH-86: Management agent should enforce format of identifiers.

New behavior:
- identity is determined by the agent, always of the form type/id for some id string.
- name is left unchanged if specified, if not specified it defaults to identity.
- qdstat uses identity, not name, since name may be set to arbitrary values by user.

git-svn-id: https://svn.apache.org/repos/asf/qpid/dispatch/trunk@1646903 13f79535-47bb-0310-9956-ffa450edef68