Fixes #166. Add raw=True when parsing passwords.

When parsing .pyrax, we should set the raw=True argument on ConfigParser.SafeConfigParser.get on key or password fields, allowing percent signs to be used there. Without this, users get InterpolationSyntaxError. Switching from SafeConfigParser to RawConfigParser would do the same thing, but it's backwards incompatible because we could have people relying on interpolation elsewhere in their config files.