Title: #1123: otptoken_yubikey.py: Removed traceback when package missing.
IPA should suggest user to install dependent packages instead
of throwing traceback. To work with IPA and Yubikey, packages
libyubikey(not in official RHEL repo) and libusb are required.
To pull the PR as Git branch:
git remote add ghfreeipa https://github.com/freeipa/freeipa
git fetch ghfreeipa pull/1123/head:pr1123
git checkout pr1123