Disable synchronous (locking) queries

This patch raises an error in the master daemon in case the user
requests a locking query; accordingly, all clients were modified to send
only lockless queries. This is short-term fix, for proper fix the
clients should be modified to submit a job when the user request a
locking query.

The other approach would be to ignore the flag passed by the client;
this would be worse as client's wouldn't get at least an error.

The possible impact of this is multiple:
  - some commands could have been not converted, and thus fail; this
    can be remedied easily
  - the consistency of commands is lost; e.g. node failover will not
    lock the node *while we get the node info*, so we could miss some
    data; this is again in the thread of atomic operations which are
    missing in the current model of query-and-act from gnt-* scripts

Reviewed-by: imsnah, ultrotter