Fix hang when user has no libusb access because of plugdev under e.g linux.

Fix hang when user has no libusb access because of plugdev under e.g linux.
Add some better sanity checking when using libusb_open and cleanup accordingly.

Fixes hang (debian 8, amd64, libusb 1.0.19):
libusb: warning [add_to_flying_list] failed to arm first timerfd (errno 9)
libusb: warning [libusb_close] internal signalling write failed, closing anyway