[RFE] distro-specific groups in functional tests

[dongsupark]

Description

#125 hot-fixed boot failure of functional tests with Debian-derivatives.

However, there are still remaining issues around functional tests to support various cases for the default user group. Following places do not care about groups.

• The systemd unit azure-init.service invokes azure-init binary without specifying custom groups with --groups.
• functional_tests.rs.

Ideally we should have general templates for the systemd service and group lists for with_groups in functional tests. Those should be converted into distro-specific files that can be used for build system. One option would be to use askama, a Jinja-like templates for Rust.

See also #106.