zodb: rework command driver for python3 compatibility

setup.py

@@ -23,7 +23,7 @@ setup(
     install_requires = ['ZODB', 'zodburi', 'zope.interface', 'pygolang >= 0.0.0.dev6', 'six', 'dateparser'],
 
     extras_require = {
-                  'test': ['pytest', 'freezegun', 'pytz'],
+                  'test': ['pytest', 'freezegun', 'pytz', 'mock;python_version<="2.7"'],
     },
 
     entry_points= {'console_scripts': ['zodb = zodbtools.zodb:main']},

tox.ini

@@ -8,6 +8,7 @@ deps	=
     pytest
     freezegun
     pytz
+    mock;python_version<="2.7"
 
     # latest ZODB from ZODB3 series
     ZODB3:  ZODB3 >=3.10, <3.11dev

zodbtools/zodb.py

@@ -51,10 +51,7 @@ Usage:
 The commands are:
 """, file=out)
 
-    cmdv = command_dict.keys()
-    cmdv.sort()
-    for cmd in cmdv:
-        cmd_module = command_dict[cmd]
+    for cmd, cmd_module in sorted(command_dict.items()):
         print("    %-11s %s" % (cmd, cmd_module.summary), file=out)
 
     print("""\