Fix pep8 error in bin/nova-manage

Also remove unused imports.

Change-Id: I6a5379ef9493fe39ba9442e809d0aeeaa97fb7b1

bin/nova-manage

@@ -54,10 +54,7 @@
   CLI interface for nova management.
 """
 
-import ast
-import errno
 import gettext
-import math
 import netaddr
 import optparse
 import os
@@ -1133,7 +1130,6 @@ class AgentBuildCommands(object):
                                'md5hash': md5hash})
 
 
-
 class GetLogCommands(object):
     """Get logging information"""