[ZODB3] setup: tests_require += zope.testrunner

Zope.testrunner is used to run ZODB tests. It was specified as explicit
dependency in buildout.cfg.  However if in SlapOS we install just
ZODB[test] zope.testrunner won't be installed.

-> Fix is by adding explicit zope.testrunner dependency into setup, so that
ZODB[test] installs it. This is the same as what ZODB5 does:

https://github.com/zopefoundation/ZODB/blob/5.6.0-14-g0eae10cd0/setup.py#L48

setup.py

@@ -197,8 +197,8 @@ setup(name="ZODB3",
       classifiers = filter(None, classifiers.split("\n")),
       long_description = long_description,
       test_suite="__main__.alltests", # to support "setup.py test"
-      tests_require = ['zope.testing', manuel_version],
-      extras_require = dict(test=['zope.testing', manuel_version]),
+      tests_require = ['zope.testing', manuel_version, 'zope.testrunner'],
+      extras_require = dict(test=['zope.testing', manuel_version, 'zope.testrunner']),
       install_requires = [
         transaction_version,
         'zc.lockfile',