Spotted while looking at different issue:
- https://uberchromegw.corp.google.com/i/chromeos/builders/guado_moblab-release/builds/882/steps/BuildPackages/logs/stdio

chromeos-adb-env-0.0.1-r2:  *  - Groupid: 272
chromeos-adb-env-0.0.1-r2:  *  - Password entry: !
chromeos-adb-env-0.0.1-r2:  *  - User list: adb
chromeos-adb-env-0.0.1-r2:  * Done with group: 'adb'.
chromeos-adb-env-0.0.1-r2:  * Adding user 'adb' to your system ...
chromeos-adb-env-0.0.1-r2:  *  - Userid: 272
chromeos-adb-env-0.0.1-r2:  *  - Groupid: 272
chromeos-adb-env-0.0.1-r2:  * A shell was specified but it does not exist !
chromeos-adb-env-0.0.1-r2:  * ERROR: chromeos-base/chromeos-adb-env-0.0.1-r2::chromiumos failed (preinst phase):
chromeos-adb-env-0.0.1-r2:  *   /bin/sh does not exist in /build/guado_moblab/
chromeos-adb-env-0.0.1-r2:  * 
chromeos-adb-env-0.0.1-r2:  * Call stack:
chromeos-adb-env-0.0.1-r2:  *     ebuild.sh, line  93:  Called pkg_preinst
chromeos-adb-env-0.0.1-r2:  *   environment, line 740:  Called enewuser 'adb'
chromeos-adb-env-0.0.1-r2:  *   environment, line 656:  Called die
chromeos-adb-env-0.0.1-r2:  * The specific snippet of code:
chromeos-adb-env-0.0.1-r2:  *               die "${eshell} does not exist in ${ROOT}";

But succeeds on 2nd round:

WARNING: The following packages failed once or more,
but succeeded upon retry. This might indicate incorrect
dependencies.
  chromeos-base/chromeos-adb-env-0.0.1-r2
@@@STEP_WARNINGS@@@