as we have an API for backup a keyspace, let's expose this feature
with nodetool. so we can exercise it without the help of scylla-manager
or 3rd-party tools with a user-friendly interface.
in this change:
* add a new subcommand named "backup" to nodetool
* add test to verify its interaction with the API server
* add two more route to the REST API mock server, as
the test is using /task_manager/wait_task/{task_id} API.
for the sake of completeness, the route for
/task_manager/{part1} is added as well.
* update the document accordingly.
* the bash completion script is updated accordingly.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
969cbb75ce