Only change uid/gid when it's not 0
Only change uid/gid when it's not 0

Only change the device uid/gid in the sandbox when it is not 0.
Otherwise, running crosvm as root makes minijail complain:

   libminijail[16370]: useless change to uid 0

BUG=none
TEST=run crosvm as root

Change-Id: Ida4b0e772ed000d3e42f77012af9d2505f64d92a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3141297
Auto-Submit: Chirantan Ekbote <35787c0e27de5c48735e07f8324823b765e8bcbc@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Fergus Dall <7ccc9f4990837cdc742a523b6780556a7c5e07d8@google.com>
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Commit-Queue: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm