[FIX] survey: use absolute paths
[FIX] survey: use absolute paths

On redirection, werkzeug converts locations from relative to absolute
URLs. Apparently the specific algorithm when given a relative *path*
changed between 0.14 and 0.15, or possibly these paths suddenly became
processed whereas before they were interpreted as absolute?

So in Werkzeug 0.14, `redirect('foo/bar')` was treated as
`redirect('/foo/bar')` but in 0.15 it's first urljoin-ed to the
current path before the redirection is effected.

This is an issue with slides, because survey's get_start_url returns
the url `survey/start/<access_token>` without a leading slash.

The result is that where with 0.14 the certification tour would do this:

    GET /slides_survey/slide/get_certification_url?slide_id=39&fullscreen=1
    GET /survey/start/<id>?answer_token=<token>

with 0.15 or above it does this:

    GET /slides_survey/slide/get_certification_url?slide_id=39&fullscreen=1
    GET /slides_survey/slide/survey/start/<id>?answer_token=<token>

Which weirdly enough doesn't work at all.

closes odoo/odoo#48982

X-original-commit: 82a23883748172c05d2562f244ffbc1558ce01fc
Signed-off-by: Xavier Morel (xmo) <0f311f41b2be8e2b5de98776566d712cdc154ca4@odoo.com>

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