Reland "mode_flag: make it empty array"

This is a reland of afe564f9a961f608d9c2b89aebe25e1c1c10063b

This change was reverted due to a bug in mod_image_for_recovery script.
That bug was fixed in crrev.com/c/2717166 and the fix was tested with
`cros tryjob -g '2713386 2713867 2713564 2717166' arkham-release-tryjob`

Original change's description:
> mode_flag: make it empty array
>
> Since bash-4.4, "${array[@]:+${array[@]}}" resolves to "", whereas
> before it was resolving to an empty array.
> _check_mount_image_flags expects an empty array, make it so.
>
> BUG=None
> TEST=unit tests
>
> Change-Id: I9de8439bcd8e20098b162c21dd03b6adcc3ac856
> Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2685277
> Commit-Queue: Sergey Frolov <sfrolov@google.com>
> Tested-by: Sergey Frolov <sfrolov@google.com>
> Reviewed-by: Mike Frysinger <vapier@chromium.org>

Bug: None
Change-Id: I98b4d334e7c5856461c4e00c1dfe6ec1a71e6be3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2713867
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Sergey Frolov <sfrolov@google.com>
1 file changed