the issue is that crosh sets up the I/O fifos to be owned/accessible only by chronos (see the `mk_fifo` command in /usr/bin/crosh).  we run shill scripts under "shill-scripts" now which has no access.

/tmp/chronos-temp-*/  700
/tmp/chronos-temp-*/fifo  644

at any rate, redirecting fd's is better than re-opening paths directly.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform2/+/fdae449fc3ce29cbf7e29e3749fcf44602d60bd6

commit fdae449fc3ce29cbf7e29e3749fcf44602d60bd6
Author: Ben Chan <benchan@chromium.org>
Date: Tue Oct 31 08:44:39 2017

modem-utilities: fix output to stderr

crosh now runs the 'modem' script via debugd (CL:675733) under the
'shill-scripts' user and group. The 'modem' now fails to write to
/dev/stderr.

BUG= chromium:779853 
TEST=Verify that running `modem set-carrier Foo` under crosh shows an error properly.

Change-Id: I6748225757122b10699aed92404180f2c8efbdd9
Reviewed-on: https://chromium-review.googlesource.com/745403
Commit-Ready: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>

[modify] https://crrev.com/fdae449fc3ce29cbf7e29e3749fcf44602d60bd6/modem-utilities/connectivity-common.sh

This bug requires manual review: M63 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), gkihumba@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform2/+/fd4a697f8222b0e34f3c06a9ca8456a7dbc61eef

commit fd4a697f8222b0e34f3c06a9ca8456a7dbc61eef
Author: Ben Chan <benchan@chromium.org>
Date: Fri Nov 03 23:47:13 2017

modem-utilities: fix output to stderr

crosh now runs the 'modem' script via debugd (CL:675733) under the
'shill-scripts' user and group. The 'modem' now fails to write to
/dev/stderr.

BUG= chromium:779853 
TEST=Verify that running `modem set-carrier Foo` under crosh shows an error properly.

Change-Id: I6748225757122b10699aed92404180f2c8efbdd9
Reviewed-on: https://chromium-review.googlesource.com/745403
Commit-Ready: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
(cherry picked from commit fdae449fc3ce29cbf7e29e3749fcf44602d60bd6)
Reviewed-on: https://chromium-review.googlesource.com/754342
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>

[modify] https://crrev.com/fd4a697f8222b0e34f3c06a9ca8456a7dbc61eef/modem-utilities/connectivity-common.sh

This issue has been approved for a merge. Please merge the fix to any appropriate branches as soon as possible!

If all merges have been completed, please remove any remaining Merge-Approved labels from this issue.

Thanks for your time! To disable nags, add the Disable-Nags label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

modem set-carrier now works on lumpy.
M-64 64.0.3282.65/(10176.34.0)