bug fixes for Lark bandwidth management

1. Add a knob for turning on/off network namespace for file transfer, by default it is turned on, to turn it off, put the following in condor configuration file: ENABLE_NETWORK_NAMESPACE_FOR_FILETRANSFER = false
2. Add another example config file used for Lark bandwidth management
3. fix bug to avoid setting ovs bandwidth rate limit to be 0
4. fix DHCP leasing cache bug