eiru_theme/views/eiru_web_login.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <template id="eiru_theme.eiru_web_login" name="Eiru Login Defaults" inherit_id="web.login">
            <xpath expr="//label[@for='login']" position="replace">
                <label for="login" class="control-label">Usuario</label>
            </xpath>
            <xpath expr="//label[@for='password']" position="replace">
                <label for="login" class="control-label">Contraseña</label>
            </xpath>
            <xpath expr="//button[@type='submit']" position="replace">
                <button type="submit" class="btn btn-primary">Iniciar Sesión</button>
            </xpath>
            <xpath expr="//p[@class='alert alert-danger']" position="replace">
                <p class="alert alert-danger" t-if="error">
                    Credenciales no válidas
                </p>
            </xpath>
        </template>
    </data>
</openerp>