Add test container based on Alpine image.

[amirouche]

It compiles sysbox, and after configuring the host docker, and running sysbox daemons, I can do:

docker run --runtime=sysbox-runc --rm -it --hostname=syscont nestybox/ubuntu-bionic-systemd

then login with admin/admin, then:

admin@syscont:~$ sudo journalctl -xe
[sudo] password for admin: 
-- Logs begin at Sat 2025-07-12 00:46:22 UTC, end at Sat 2025-07-12 00:46:38 UTC. --
Jul 12 00:46:22 syscont systemd-journald[188]: Journal started
-- Subject: The journal has been started
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- The system journal process has started up, opened the journal
-- files for writing and is now ready to process requests.
Jul 12 00:46:22 syscont systemd-journald[188]: Runtime journal (/run/log/journal/1b4e89a5b1164946adc9c370510ccd63) is 820.0K, max 6.4M, 5.6M free.
-- Subject: Disk space used by the journal
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- Runtime journal (/run/log/journal/1b4e89a5b1164946adc9c370510ccd63) is currently using 820.0K.
-- Maximum allowed usage is set to 6.4M.
-- Leaving at least 9.6M free (of currently available 63.1M of disk space).
-- Enforced usage limit is thus 6.4M, of which 5.6M are still available.
-- 
-- The limits controlling how much disk space is used by the journal may
-- be configured with SystemMaxUse=, SystemKeepFree=, SystemMaxFileSize=,
-- RuntimeMaxUse=, RuntimeKeepFree=, RuntimeMaxFileSize= settings in
-- /etc/systemd/journald.conf. See journald.conf(5) for details.
Jul 12 00:46:22 syscont systemd[1]: systemd-journald.service: Failed to add fd to store: Operation not permitted
Jul 12 00:46:22 syscont systemd[1]: systemd-journald.service: Failed to add fd to store: Operation not permitted
Jul 12 00:46:22 syscont systemd[1]: systemd-journald.service: Failed to add fd to store: Operation not permitted
Jul 12 00:46:22 syscont systemd-journald[188]: Runtime journal (/run/log/journal/1b4e89a5b1164946adc9c370510ccd63) is 820.0K, max 6.4M, 5.6M free.
-- Subject: Disk space used by the journal
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- Runtime journal (/run/log/journal/1b4e89a5b1164946adc9c370510ccd63) is currently using 820.0K.
-- Maximum allowed usage is set to 6.4M.
-- Leaving at least 9.6M free (of currently available 63.1M of disk space).
-- Enforced usage limit is thus 6.4M, of which 5.6M are still available.
-- 
-- The limits controlling how much disk space is used by the journal may
-- be configured with SystemMaxUse=, SystemKeepFree=, SystemMaxFileSize=,
-- RuntimeMaxUse=, RuntimeKeepFree=, RuntimeMaxFileSize= settings in
-- /etc/systemd/journald.conf. See journald.conf(5) for details.
Jul 12 00:46:22 syscont systemd[1]: systemd-journald.service: Failed to add fd to store: Operation not permitted
Jul 12 00:46:22 syscont systemd[1]: systemd-journald.service: Failed to add fd to store: Operation not permitted
Jul 12 00:46:22 syscont systemd[1]: systemd-journald.service: Failed to add fd to store: Operation not permitted
Jul 12 00:46:22 syscont systemd-resolved[295]: Positive Trust Anchors:
Jul 12 00:46:22 syscont systemd-resolved[295]: . IN DS 19036 8 2 49aac11d7b6f6446702e54a1607371607a1a41855200fd2ce1cdde32f24e8fb5
Jul 12 00:46:22 syscont systemd-resolved[295]: . IN DS 20326 8 2 e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
Jul 12 00:46:22 syscont systemd-resolved[295]: Negative trust anchors: 10.in-addr.arpa 16.172.in-addr.arpa 17.172.in-addr.arpa 18.172.in-addr.arpa 19.172.in-addr.arpa 20.172.in-ad
dr.arpa 21.172.in-addr.arpa 22.172.in-addr.arpa 23.172.in-addr.arpa 24.172.in-addr.arpa 25.172.in-addr.arpa 26.172.in-addr.arpa 27.172.in-addr.arpa 28.172.in-addr.arpa 29.172.in-a
ddr.arpa 30.172.in-addr.arpa 31.172.in-addr.arpa 168.192.in-addr.arpa d.f.ip6.arpa corp home internal intranet lan local private test
Jul 12 00:46:22 syscont systemd-resolved[295]: Using system hostname 'syscont'.
Jul 12 00:46:22 syscont systemd-sysctl[187]: Couldn't write '1' to 'kernel/yama/ptrace_scope', ignoring: No such file or directory
Jul 12 00:46:22 syscont systemd[1]: systemd-journald.service: Failed to add fd to store: Operation not permitted
Jul 12 00:46:22 syscont systemd[1]: systemd-journald.service: Failed to add fd to store: Operation not permitted
Jul 12 00:46:22 syscont systemd-logind[460]: New seat seat0.
-- Subject: A new seat seat0 is now available
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- Documentation: https://www.freedesktop.org/wiki/Software/systemd/multiseat
-- 
-- A new seat seat0 has been configured and is now available.
Jul 12 00:46:25 syscont login[474]: pam_unix(login:session): session opened for user admin by LOGIN(uid=0)
Jul 12 00:46:38 syscont sudo[505]:    admin : TTY=console ; PWD=/home/admin ; USER=root ; COMMAND=/bin/journalctl -xe

but make test errors, and among the unit tests only make test-mgr succeeds.