Handle exception when invalid config file is specified
Handle exception when invalid config file is specified

When an invalid configuration file is specified (i.e. python
file), bandit prints a traceback. This change handles the
yaml parse exception and informs the user the configuration file
is invalid.

Change-Id: Id057c19ebddb16316c8b6e80cead51058a6172fd
Closes-bug: #1435422

austin987/bandit,pombredanne/bandit,chair6/bandit,stackforge/bandit,stackforge/bandit,pombredanne/bandit