People might not have read all the documentation and might not expect their ssh configuration
and specially keys to be changed. Adding this warning will inform them before it happens.

Reviewed-by: iustinp

Change this to have the exact same parameters as OpQueryInstances.

Also fix burnin which is broken since r146.

Reviewed-by: imsnah

Now that LUQueryNodes supports all the functionality of LUQueryNodeData,
let's migrate gnt-node.ShowNodeConfig to use it and remove all traces of
OpQueryNodeData and LUQueryNodeData.

Reviewed-by: imsnah

LUQueryNodes it's very similar to LUQueryNodeData, but it lacks two
features:
  - instance list (it has count though), both primary and secondary
  - selective node listing

In order to support these features, we change it to return raw values
instead of stringified ones (like the recent change to LUQueryInstances)
and to support query-ing of a restricted set of nodes.

This CL also modifies the gnt-node script to conform to the new protocol
and the opcode OpQueryNodes to support the new "nodes" attribute.

Reviewed-by: imsnah

Since the table generation might be useful elsewhere, let's change it to
return the data instead of directly printing it.

Its callers have also been updated.

Reviewed-by: imsnah

This changes the raising of exceptions from:
  raise Exception, value
to
  raise Exception(value)

as the first form will be removed in python-3000 and the second form is
preferred now.

The changes also involve a few cases of changing from raising standard
exceptions and use our own ones.

The new version also fixes many pylint-generated warnings, especially in
ganeti-noded where I changed many methods to @staticmethod.

There is no functionality changed (barring any bugs).

Reviewed-by: iustinp

- Create all --output options using a constant
- Put node checking code from opcodes into a single function
- Do the same for output fields

Reviewed-by: iustinp