Some of these can only run as root on a real system with access to loop
devices. They are skipped when running in a container.
(cherry picked from commit 063a1770e1)
This adds empty __init__.py to tests so that a lib.py library of helper
functions can be imported from the tests.
Add captured_output to use with composer-cli tests to capture stdout/err
output from the functions.
(cherry picked from commit eeae331ba0)