Added command-line parser to parse arguments passed to the script

I have done the following changes :
- Added a main() to the script
- Added command-line parsing ability
- Added command-line option "-m" or "--mgmt-intf" to allow the user to specify Management interface instead of the default eth0
- Added command-line option "-i" or "--internal-intf" to allow the user to specify Internal interface instead of the default eth1