Support running "beah" test harness in a Docker container

Commit bea3655 added support for running the test harness in a docker
container. However, the "beah" test harness needed some additional
work. This patch does that.

Non-systemd docker images are not supported yet.

Bug: 1131388
Change-Id: If49372fa879c91b997ff79d84a8458c5241fa136