metadata stored with swift object and xbcloud list command

Currently when using innobackupex/xbcloud together to create incremental backups, the checkpoint metadata from the previous backup must be redirected to a separate directory using --extra-lsndir. The next incremental backup must extract the to_lsn from the previous backups metadata in order to proceed. This makes the incremental backup process and the restore process difficult to manage and explain to the user.

In order to make F,i,i,i backups easier to create and restore, meta data can be stored along with each swift object:

1) iso timestamp
2) backup type
3) from_lsn
4) to_lsn
5) host
6) source dir

xbcloud would need to parse this information from the stream at the end of the PUT or maybe an additional block of metadata sent to standard output after the stream.

xbcloud would then use the Swift API Object Metadata POST command to store the time,type lsn's, host and src dir along with the xbstream archive object.

Another possibility would be to integrate xbcloud directly into innobackupex allowing it to manage the swift metadata attachments and retrieve the last to_lsn from the object container.

In addition to storing the metadata, xbcloud could implement a simple show/list feature that would read back the object names and meta data from a container. This will assist in the restore process as well as making it easier to determine the to_lsn from the last backup for the next incremental.