`eend 0` does effectively nothing, so let's remove it

[adrelanos]

eend() {
  local retval="${1:-0}"
  shift
  if [ "$retval" -gt 0 ]; then
    printf " %s-> Failed (rc=%s)%s\\n" "${BAD}" "${retval}" "${NORMAL}"
  fi
  return "$retval"
}

eend 0 just results in return 0 which doesn't do anything.

In preparation of #224 for code simplification it would be best to remove these.

A very few cases are a tiny bit more complex.

      if cp "$AUTHORIZED_KEYS_SOURCE" "$AUTHORIZED_KEYS_TARGET" ; then
        eend 0
      else
        eerror "Error: copying '$AUTHORIZED_KEYS_SOURCE' to '$AUTHORIZED_KEYS_TARGET' failed"
        eend 1
        bailout 1
      fi

Could rewrite to:

      if ! cp "$AUTHORIZED_KEYS_SOURCE" "$AUTHORIZED_KEYS_TARGET" ; then
        eerror "Error: copying '$AUTHORIZED_KEYS_SOURCE' to '$AUTHORIZED_KEYS_TARGET' failed"
        eend 1
        bailout 1
      fi