Specifying nodesets in ID attributes in not allowed by XML spec

[rezib]

Example of error on XML validation:

# xmllint --valid --noout /etc/slurm-web/racks.xml
/etc/slurm-web/racks.xml:15: element nodeset: validity error : Syntax of value for attribute id of nodeset is not valid
          <nodeset id="pocn[001-036]" type="nx360" posy="3" />
                                                            ^
/etc/slurm-web/racks.xml:16: element nodeset: validity error : Syntax of value for attribute id of nodeset is not valid
          <nodeset id="pocn[037-072]" type="nx360" posy="23" />
                                                             ^

Spec is here: http://www.w3.org/TR/xml/#sec-attribute-types

The id attribute must renamed, eg. nodes.