Chrome Version: 
OS: Chrome OS

What steps will reproduce the problem?
(1) Build and boot an amd64-generic image.
(2) Run "chromeos-install" without arguments

What is the expected result?
System should complain that "--dst" was required.

What happens instead?
You get the following output
    cros-disks stop/waiting
    /usr/sbin/chromeos-install: 258: /usr/sbin/chromeos-install: dev: parameter not set


The root cause of the problem is apparently this code in
chromeos-common.sh:

get_fixed_dst_drive() {
  local dev rootdev

  if [ -n "${DEFAULT_ROOTDEV}" ]; then
    # No " here, the variable may contain wildcards.
    for rootdev in ${DEFAULT_ROOTDEV}; do
      dev="/dev/$(basename "${rootdev}")"
      if [ -b "${dev}" ]; then
        break
      else
        dev=""
      fi
    done
  fi
  echo "${dev}"
}

If DEFAULT_ROOTDEV isn't set, then "${dev}" will be uninitialized.
The script runs with `-u` set, so the unset variable is an error.