node: Make OVS switches reconnect quickly

Ordinarily, OVS switches back off when they can't reach their controllers.
Under the type of scenarios where Mininet is used, I think this is
probably just inconvenient.  This patch set controllers to attempt to
reconnect every second.
Add NAT script to examples.
Don't flush ALL routes and enable OPTIONAL default route/gw

fixes #152 hopefully
Merge pull request #150 from MurphyMc/ovs_fast_reconnect

node: Make OVS switches reconnect quickly
Separate VM finalization as install.sh -tc
vm_cleanup: add apt-get autoremove, and zero disk blocks
Use dd to zero out disk space (hopefully faster)
"file blocks" -> "disk blocks"
install.sh: Make OF1.3 Netbee location cmd-line configurable

If NBEEURL is defined when running install.sh, use that location.

Enables use of a local mirror for netbee download.

Thanks to David Erickson for the code.
topo: add __getitem__ for Graph

Commit 65c35b65 'Remove networkx dependency' broke this line from RipL:

    nodes = [n for n in self.g[name] if self.layer(n) == layer]

To work around this, RipL code would have to be changed to something
like this:

    nodes = [n for n in self.g.data[name] if self.layer(n) == layer]

...which would use an internal variable, data.

It seems cleaner to add this one little feature from NetworkX Graph objects.
topo: make new minimal Graph object a Graph, not a DiGraph

Fixes another Graph regression relative to NetworkX.

RipL broke because the NetworkX Graph object that was used previously
for topologies is an undirected graph:

>>> import networkx as nx
>>> g=nx.Graph()
>>> g.add_edge(0,1)
>>> g[1]
{0: {}}
>>> g[0]
{1: {}}

There is a separate DiGraph object in NetworkX for directed behavior.

The minimal replacement previously implemented DiGraph behavior.

>>> from mininet.topo import Graph
>>> g2=Graph()
>>> g2.add_edge(0,1)
>>> g2[0]
[1]
>>> g2[1]
[]

This commit restores undirected graph behavior.
Add script completion message
Update archive for 13.04
Fix typo.
Fix setDefaultRoute to work with passed parameters.
Replace /etc/hostname entirely; clarify sources.list edit
Clean up (and fix) OVSSwitch fast reconnect
Minor comment change and text change.
Add Switch.connected() and OVSSwitch.controllerUUIDs()
Fix some pylint messages.