This is first step in supporting node aliases. It adds a table
that automatically assigns aliases to nodes inserted into the table.
Change-Id: Ibdf40097c3c1e5b371500203f8db203505a48adc
to metabase
* EncryptedMetainfoEncryptedKey added to CommitSegment and
UpdateMetadata request
* EncryptedMetainfoEncryptedKey returned with GetObject response and all
delete responses
* EncryptedMetainfoEncryptedKey returned with object iterator results
Change-Id: I917541ab5f3e1863bc8f238d17a15fbf72a23025