germ, libchromeos: Add --interactive, --shell cmdline options.

BUG=brillo:422
TEST=Manual: deploy to device,
TEST=germ --name=yes --executable=/usr/bin/yes --interactive prints 'y's.
TEST=germ --name=yes --executable=/usr/bin/yes --shell
TEST=$ id shows random uid/gid.
TEST=$ ps shows correct process ids.

Change-Id: Icd01474e7c1afb047450d62a27c97a6a734cb892
Reviewed-on: https://chromium-review.googlesource.com/255313
Trybot-Ready: Jorge Lucangeli Obes <jorgelo@chromium.org>
Tested-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Utkarsh Sanghi <usanghi@chromium.org>
Reviewed-by: Lee Campbell <leecam@chromium.org>
Commit-Queue: Jorge Lucangeli Obes <jorgelo@chromium.org>
2 files changed