setup: Install `ZEO[test]` when testing.

`ZEO[test]` should be installed when testing, so that `zope.testing` is
installed.
Otherwise, an import error may be raised when running the test if
`zope.testing` has not been manually installed.

--------
kirr:

Adjust tox.ini to no longer install zope.testing explicitly since we are
now requesting ZEO[test] under our own tests extra, and tox.ini installs
.[test] as the primary package.

/reviewed-by @kirr
/reviewed-on nexedi/wendelin.core!27

setup.py

@@ -401,7 +401,7 @@ setup(
                      'pytest',
                      'scipy',
                      'neoppod',     # lib/tests/test_zodb.py
-                     'ZEO',         # lib/tests/test_zodb.py
+                     'ZEO[test]',   # lib/tests/test_zodb.py
                     ],
     },
 

tox.ini

@@ -26,10 +26,6 @@ deps    =
     # neo.tests also imports MySQLdb unconditionally
     neo:    mysqlclient
 
-
-    # zeo: ZEO is already required by ZODB, but for testing utilities from ZEO we also need:
-    zeo:    zope.testing
-
     numpy116: numpy >=1.16.0, <1.17.0
     numpy115: numpy >=1.15.0, <1.16.0