To generate a barcode using that way you need to have installed reportlab dependency and the module 'report' that it's auto-installed when base and web modules are installed, check those prerequisites and if they are ok you could always test in the browser your barcode image using this url in your case:

http://localhost:8069/report/barcode/Code128/test-0001

that will return you the barcode image generated, If some other error shows in the logs post it here. If the barcode not get generated and the logs doesn't show anything, then you need to debug what happens at /openerp/addons/report/controllers/main.py on the report_barcode method.

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I test it and debug it and seems that you cannot do that because the request to the controller came with no session_id and also no database to use and get dropped with a 404. Your alternative could be to directly generate the barcode image using the same code of the barcode controller but used from a report parser. Define a function in a parser like:

import base64
from openerp.report import report_sxw
from reportlab.graphics.barcode import createBarcodeDrawing

class barcode_report_parser(report_sxw.rml_parse):
    def __init__(self, cr, uid, name, context):
        super(barcode_report_parser, self).__init__(cr, uid, name, context=context)
        self.localcontext.update({
            'barcode': self.barcode,
        })
    def barcode(self, type, value, width=600, height=100, humanreadable=0):
        width, height, humanreadable = int(width), int(height), bool(humanreadable)
        barcode_obj = createBarcodeDrawing(
            type, value=value, format='png', width=width, height=height,
            humanReadable = humanreadable
        )
        return base64.encodestring(barcode_obj.asString('png'))

In the report template define your image like this:

<img t-att-src="'data:image/png;base64,%s' % barcode('Code128','test-0001')" style="width:100%;height:25px"/>