Fix XML UnicodeEncode serialization error

The generic Nova XMLSerializer code will currently attempt
to cast to str the value for all leaf nodes. This patch
ensures that no attempt is made to convert unicode which
can cause a UnicodeEncode error. We don't need to convert
unicode for XML text and regardless we encode to UTF-8 at
a later point.

Change-Id: I8135d2b9a67db62b0eafdd301b7fdb67a5dd72cc
Closes-Bug: #1279172
Removes unused code from wsgi _to_xml_node

Removes support for metadata list_collections and dict_collections
as it is no longer used. Looks like it was last used in the previous
implementation of the Nova API framework (eg before the current V2 one)

Change-Id: I314b13816cdcf51f04926ca9eec67cac765cc893
Open Kilo development

Bump pre-version to 2015.1 to formally open master branch to Kilo
development.

Change-Id: Ib634eb7acb64ff1d7be49852972295074b11557a
Merge "Open Kilo development"
Merge "Fix XML UnicodeEncode serialization error"
Merge "Removes unused code from wsgi _to_xml_node"