Also switch from print to info statements, to enable a non-verbose
clean.  Instead of 'mnclean', now run 'mn -c'.

Now you can pass a topology name followed by params.  For example, to
create a switch with 3 hosts:

  sudo mn --topo single,3

Also print warning if user chooses a loglevel that will hide CLI output.

We need to figure out how to specify the IP addresses for the
routed control network. For now I'm going back to 192.168.12x.y

Also changed controller params to use IP strings rather than
numbers. However, we still need to clarify what ControllerParams
is actually for.

Still could be better though.... and we need more topology
examples.

Later we may wish to optimize this so that the arg lists are
not created if the logging level is too low.

Also changed the str format for nodes to use str() rather
than repr() so we don't end up with extraneous quotes.

Also tweaked cmd/cmdPrint to make them more beautiful and functional,
and a few other minor changes, such as using a new idiom for verbose.

These changes support reinstating the examples.