IVSSwitch: support batch shutdown

Not a single command like the OVS one, but it still greatly decreases the
shutdown time.

This does assume that stop() is called after batchShutdown(), which is true in
the current mininet code.
net: allow batch shutdown of multiple types of switches

Each switch class will be called to shutdown its own instances.
IVSSwitch: add an option to control the --verbose flag
Merge pull request #309 from rlane/ivs-batch-shutdown

support batch shutdown for IVS
Merge pull request #310 from rlane/ivs-verbose

IVSSwitch: add an option to control the --verbose flag
slight refactoring of util/vm/build.py to make it more extensible
build.py: making ovf generation more generic
fixed netParse bug that caused mininet crash when no ip prefix was specified
Merge pull request #313 from cdburkard/master

ovs port numbering bug fix
Merge pull request #316 from cdburkard:patches/fix_remote_ip

fixed netParse bug that caused mininet crash when no ip prefix was specified
Whitespace changes in OVSSwitch.
Merge pull request #317 from cdburkard/patches/cleanup

added code to kill stale mininet processes
Merge pull request #315 from cdburkard/patches/fix_bindpy

Added support for mount namespaces in bind.py
Adding listen socket to UserSwitch when there is no listenPort set
Merge remote-tracking branch 'upstream/master'