Typo

Fix additional_buildout_parametr_list to read
additional_buildout_parameter_list
Add XXX
Factor slapobject test mixin.
Add XXXs
Simplify, factor slapobject test mixin

- Clearly define the imports
- Refactor specific mockup
Add slapobject mockups
Add Helpers in slapobject test
Add testsuite for SlapObject.Partition
Externalize supervisor stuff from Partition.install()
Rewrite backward compatiblity about 'template.cfg'

- Raise early
- Also add sanity checks and correct output errors.
- This was outputting bad error message in some cases, making debugging
impossible.
Add check for Software Release directory existence.
Add missing import