This allows “gnt-node list” to show the difference between modes marked
offline and nodes with e.g. RPC errors (“(nodata)”). node1 is the
master, node2's node daemon crashed and node3 is marked offline:

$ gnt-node list -o name,offline,dtotal,dfree
Node              Offline    DTotal     DFree
node1.example.com N            1.3T      1.3T
node2.example.com N        (nodata)  (nodata)
node3.example.com Y       (offline) (offline)

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

“kind” is already used in the field definition. “what” seems to
be a better fit for the calls (“what should be queried?”).

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

While starting to implement this, I found a number of deficiencies:

- Drop regular expressions. As it turned out, only very few fields for
  instances used them, all of which can easily be turned into static
  field names.
- Use two separate calls with a request and response description each.
- Add forgotten list of fields to query request.
- Add value status for case where a field is not available for an item,
  e.g. NIC 3 for an instance with only one network interface.
- Add "timestamp" field type.
- Updated examples.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>