OVS install Ubuntu packages

IVSSwitch: wait for ivs to terminate before tearing down node

persistent command history

This was a problem when running IVS in a container. IVS would begin the process
of closing controller connections on receiving SIGTERM, but often mininet would
have continued on and removed the control network interface from the container
before it could send the FIN. The controller wouldn't know the connection had
been closed until it timed out much later.

Saves readline history to ~/.mininet_history.

(pending) mnexec: mount sysfs in each container

    This argument expect a parameter which is the version number of OVS you wish to install.
    install.sh -V 2.0.0

    What is nice that I tested, is that you can keep running the above to change
    which OVS version you want to test with.  Also, if a new version of OVS
    is released, just run the above again specifying the new version number.

    The version number must match the version number in the tarball file name
    like openvswitch-2.0.0.tar.gz.  In this case, the version specified
    must be 2.0.0.

fixes #279

This saves about 10 seconds for a 200 switch network.

This seems slightly ugly, but it has bitten many people.

Closes #268

Add notes about specific release branches.

adjust regex for finding mininet's links during cleanup

closes #268

Close the file when done with it.

fixup: useless_parenthesis

Add spaces.

OK...

print error messages when making interfaces

userspace switch can be reached on unix port by dpctl

This is added because we install Ubuntu from a serial console.
Fixes #265

don't crash when link is TCLink but without options

fixup: unresolved_references

without this, thereis no indication in Mininet that creating an
interface has failed. for example, this may happen when the interface
name is too long (longer than IFNAMSIZ, which is 16 chars).

caused by optimized return in link.py#275 in TCIntf.config()

link names of the form "a-b-ethN" were previously interpreted
as "b-ethN". this change accepts link names with a dash, and
requires N to only contain digits.

should facilitate importing 64-bit image

fixes #261