handles keyboard interrupt

When an user intentionally provides an keyboard interrupt, neutronclient
throws the entire traceback on to the terminal instead of handling it.
neutronclient will now handle the keyboard interrrupt and provides an crisp
message on to the terminal.

Change-Id: I55a85cd4bfcbf26d81e5678b6f4aed3d1c288467
Closes-Bug: #1367283
Merge "handles keyboard interrupt"