to-json support for list-ns-osds

[JeffreyDevloo]

Problem description

This command is the only to check whether a namespace is ready to receive objects.
Processing the plain text output from it is a bit of a hassle

Example output:

root@ovs01:~# alba list-ns-osds --config arakoon://config/ovs/arakoon/hddBackend-abm/config?ini=%2Fopt%2FOpenvStorage%2Fconfig%2Farakoon_cacc.ini ffc00c91-5445-4486-8b5c-9fd2c8a68d81
osds : [(0L, Albamgr_protocol.Protocol.Osd.NamespaceLink.Active);
  (1L, Albamgr_protocol.Protocol.Osd.NamespaceLink.Active);
  (2L, Albamgr_protocol.Protocol.Osd.NamespaceLink.Active);
  (3L, Albamgr_protocol.Protocol.Osd.NamespaceLink.Active);
  (4L, Albamgr_protocol.Protocol.Osd.NamespaceLink.Active);
  (5L, Albamgr_protocol.Protocol.Osd.NamespaceLink.Active);
  (6L, Albamgr_protocol.Protocol.Osd.NamespaceLink.Active);
  (7L, Albamgr_protocol.Protocol.Osd.NamespaceLink.Active);
  (8L, Albamgr_protocol.Protocol.Osd.NamespaceLink.Active);

This is currently blocking us as sometime after the creation of a namespace we get 'NoSatisfiablePolicy' exception for uploading an object (right after its creation)