api: Wire up storage_service removal_status and force_remove_completion
api: Wire up storage_service removal_status and force_remove_completion

They are used by nodetool removenode:

$ nodetool removenode force
$ nodetool removenode status

For example:

$ nodetool removenode status
RemovalStatus: Removing token (-8969872965815280276). Waiting for
replication confirmation from [127.0.0.3,127.0.0.1].

$ nodetool removenode force
RemovalStatus: No token removals in process.

Tested with:

1)
- start 3 nodes
- inject data with
  cassandra-stress write no-warmup cl=TWO n=2000000 -schema 'replication(factor=2)'
- kill -9 node2
- wait for node2 to be in DOWN state
- run nodetool removenode host2_host_id on node1

2)
- start 3 nodes
- inject data with
  cassandra-stress write no-warmup cl=TWO n=2000000 -schema 'replication(factor=2)'
- kill -9 node2
- wait for node2 to be in DOWN state
- run nodetool removenode host2_host_id on node1
- kill -9 node3
- nodetool removenode will wait forever since node3 is gonne, node3
  will never send the replication confirmation to node1
- run nodetool removenode force on node1
  nodetool removenode completes with the following error:
    $ nodetool removenode 31690b82-ebb0-4594-8bcf-1ce82b6e0f6e
    nodetool: Scylla API server HTTP POST to URL
    '/storage_service/remove_node' failed: nodetool removenode force is called by user
  nodetool removenode force completes sucessfully
    $ nodetool removenode force
    RemovalStatus: Removing token (-9171569494049085776). Waiting for
    replication confirmation from [127.0.0.3,127.0.0.1].

Fixes 1135.

scylladb/scylla,duarten/scylla,kjniemi/scylla,scylladb/scylla,kjniemi/scylla,duarten/scylla,raphaelsc/scylla,avikivity/scylla,avikivity/scylla,kjniemi/scylla,scylladb/scylla,scylladb/scylla,raphaelsc/scylla,avikivity/scylla,duarten/scylla,raphaelsc/scylla