Following approach used for pygolang in the previous patch lets add
testing support for zodbtools:

- Add zodbtools/buildout-dev.cfg that overrides [zodbtools] to use the
  software from git checkout.

- Add zodbtools/test<X>.cfg that is software-release to create a test
  instance to be run under testnode. To help itself on this task this
  software release uses just-added stack/nxdtest.cfg and
  [python-interpreter] from pygolang, so the code in zodbtools is
  minimal.

Zodbtools can be tested against both ZODB4 and ZODB5 because we still
use ZODB4 as our primary ZODB version, but it is no longer supported by
upstream which considers only ZODB5 as current.