<openerp>
  <data>
    <record id="res_config_view_base" model="ir.ui.view">
      <field name="name">res.config.view.base</field>
      <field name="model">res.config</field>
      <field name="type">form</field>
      <field name="arch" type="xml">
        <form>
          <group string="res_config_contents">
          </group>
          <separator string="" colspan="4"/>
          <field name="progress" widget="progressbar" nolabel="1" colspan="1"/>
          <label string="" colspan="1"/>
          <group colspan="2" col="4">
            <button name="action_skip" icon="gtk-cancel" special="cancel"
                    type="object" string="Skip"/>
            <button name="action_next" icon="gtk-ok"
                    type="object" string="Next"/>
          </group>
        </form>
      </field>
    </record>
  </data>
</openerp>

<openerp>
  <data>
    <record id="res_config_view_base" model="ir.ui.view">
      <field name="name">res.config.view.base</field>
      <field name="model">res.config</field>
      <field name="type">form</field>
      <field name="arch" type="xml">
        <form>
          <group string="res_config_contents">
          </group>
          <separator string="" colspan="4"/>
          <field name="progress" widget="progressbar" nolabel="1" colspan="1"/>
          <label string="" colspan="1"/>
          <group colspan="2" col="4">
            <button name="action_skip" icon="gtk-goto-last" special="cancel"
                    type="object" string="Skip"/>
            <button name="action_next" icon="gtk-go-forward"
                    type="object" string="Next"/>
          </group>
        </form>
      </field>
    </record>
  </data>
</openerp>

Change default icons on res.config view buttons
[imp] Change default icons on res.config view buttons