runbot_buildout uses deprecated bootstrap.py

[hbrunn]

all of https://github.com/OCA/runbot-addons/blob/11.0/runbot_buildout/models/runbot_build.py#L237 and following is wrong, and will fail by now as the master branch of buildout deprecated the bootstrap script. (fast fix is to change master to 2.x)

The right thing to do here is pip install zc.buildout, and adapt https://github.com/OCA/runbot-addons/blob/11.0/runbot_buildout/models/runbot_build.py#L101 to call the buildout command in $PATH. This might involve having virtualenvs per build (very non-trivial I think), or make zc.buildout in both python versions a prerequisite of the module.

As the perpetrator of this miss I feel responsible for reporting it, but won't fix it myself as I'm on an extended leave. So I hope @NL66278 @janverb @thomaspaulb will come up with a fix :-)