Refactor adding SI metadata

Change-Id: I676e52a89ce132ac3b56336b5ce9d38762d4a3bc
Fixed a bug in the metadata refactor code.

Merge branch 'extension-OS-SI' of github.com:rackspace-titan/nova into extension-OS-SI

Change-Id: I4e68cb8d9d07a35d88b617e2a6655c7a43d32e32
Merge branch 'extension-OS-SI' of github.com:rackspace-titan/nova into extension-OS-SI
Merge pull request #14 from esheffield/extension-OS-SI

Refactor adding SI metadata