Add datastore filter to backup-list

This fix enhances the backup-list command to optionally receive
a datastore name or ID to filter the backup list by. The filter
is sent as a query string.

To attach the query string to the URL and have it still work with
the URL for pagination, i have made some changes in the way url
with query strings are constructed. This includes the pagination
URL.

partially implements: blueprint backup-metadata

Change-Id: I0b9ef3ec7f51ed76517a22f9c0edfdce3694a36f
Merge "Add datastore filter to backup-list"