Fix 'cgroups not mounted' error in U12.10

'mount' shows something slightly different in Ubuntu 12.10:

cgroup on /sys/fs/cgroup type tmpfs (rw,uid=0,gid=0,mode=0755)

Note the lack of a plural on first word cgroup, which has changed.

Still mounted at /sys/fs/cgroup, so check for both possibilities
when instantiated CPU-limited hosts.

mininet/util.py

@@ -361,7 +361,8 @@ def mountCgroups():
     mounts = quietRun( 'mount' )
     cgdir = '/sys/fs/cgroup'
     csdir = cgdir + '/cpuset'
-    if 'cgroups on %s' % cgdir not in mounts:
+    if ('cgroup on %s' % cgdir not in mounts and
+            'cgroups on %s' % cgdir not in mounts):
         raise Exception( "cgroups not mounted on " + cgdir )
     if 'cpuset on %s' % csdir not in mounts:
         errRun( 'mkdir -p ' + csdir )