software/slapos-sr-testing: add erp5-py3

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WIP ERP5: XXX dumps() parameter for longrequest promise 

Not sure why it was OK on python2 and not sure if this has to be done
or the promise code needs to cast the results of getConfig()

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py3: do not enable NEO test yet 

at this point they all fail after long timeouts, because neo does not
support py3 yet

stack/erp5: version up APacheDEX 2.0 (py3 only)
Co-authored-by: Kazuhiko SHIOZAKI <kazuhiko@nexedi.com>
Co-authored-by: Arnaud Fontaine <arnaud.fontaine@nexedi.com>
Co-authored-by: Bryton Lacquement <bryton.lacquement@nexedi.com>