Ensure script exits with failure status on failure

[jsherwood0]

To make this script easily wrappable by other scripts, it should return a failure status when it fails so that logic like the following can work:

# inside loop that iterates through computers in an AD OU
if kerbrute -domain "${DOMNAME}" -user "${COMPNAME}\$" -password "${COMPNAME:0:14}" -dc-ip $DCIP; then
  echo "${COMPNAME} - VULNERABLE - Pre2k default password" | tee -a $OUTFILE
elif kerbrute -domain "${DOMNAME}" -user "${COMPNAME}\$" -password "" -dc-ip $DCIP; then
  echo "${COMPNAME} - VULNERABLE - Blank default password" | tee -a $OUTFILE
fi