This parameter is already supported by the other switch classes.

test_hifi.py currently fails for OVS when datapath=user -
we should look at this and fix it.

fixes #199

----------
*** c0 : ('echo A | telnet -e A 127.0.0.1 6633',)
telnet: connect to address 127.0.0.1: Connection refused
Telnet escape character is 'A'.
Trying 127.0.0.1...
Unable to contact the remote controller at 127.0.0.1:6633
----------

Use files instead of sysctl to set limits

fixes #184

Fixed locals bug (now they are persisent across calls)

Updated Mininet to be more compliant with dict
Fixes #182

fixes #168

fixes #172

fixes #173

fixes #176

Extended LinearTopo to support mulitple hosts per switch

This change uses the `Node.cmd` method instead of `Popen`. The `cmd` method
sends the input to a shell which may be in another namespace (if --innamespace
is in use), while `Popen` would always run in the root namespace.

IVS needs to be sent SIGTERM so it has a chance to clean up the kernel
datapath.

Changed mountCgroups to use the file /proc/mounts (instead of the
current case where it uses the less reliable
(http://www.mail-archive.com/lxc-devel@lists.sourceforge.net/msg00455.html)
/etc/mtab thorugh the mount program