plans: set sbin-inclusive PATH for test execution (fix tmt 1.75.0 regression)

[andrewlukoshko]

Problem

The compose-tests suite started failing on the same commit that previously passed:

• Pass: run 26945759392 (Jun 4) — 133/133 tests passed
• Fail: run 27097580353 (Jun 7) — ~18 legacy/ng tests fail

Both runs are the same commit (1b49e3e) with the same test scripts, so the regression is environmental.

Every failing test fails with command not found (or a missing artifact downstream of one) on a binary that lives in /usr/sbin or /sbin:

Test(s)	Missing command
p_audit	auditctl (auditd never starts)
p_bridge-utils, p_network, p_tcpdump	ip, ifconfig, tcpdump
p_openssh, p_passwd, p_shadow-utils, p_dovecot	useradd, userdel, usermod, runuser
p_initscripts, p_tftp-server	service
p_nfs, p_vsftpd	exportfs, setsebool
p_cracklib	cracklib-check
p_logwatch, p_iptraf, p_mdadm	logwatch, iptraf-ng, mdadm
/tests/podman	useradd, usermod, userdel
/tests/libbpf-tools	bpf-* helpers

Root cause

The workflow pip installs tmt unpinned. Between the two runs it moved 1.74.0 → 1.75.0, which shipped teemtee/tmt#4900 — "Do not populate the default command environment with tmt process envvars." Commands run on the guest no longer inherit tmt's os.environ, so the runner's PATH (which included /usr/sbin:/sbin) is no longer forwarded. The legacy t_functional scripts and several ng tests call privileged tools by bare name and depend on sbin being on PATH.

Fix

Set an explicit sbin-inclusive PATH in the legacy and ng plan environments, making the suite independent of tmt's env-forwarding behavior (robust across future tmt upgrades).

PATH: "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

[andrewlukoshko]

Follow-up: added `HOME: "/root"` to both plan environments.

The PATH fix cleared all the command not found failures, but p_go remained red — same tmt 1.75.0 regression (teemtee/tmt#4900), this time because HOME is no longer forwarded:

build cache is required, but could not be located: GOCACHE is not defined and neither $XDG_CACHE_HOME nor $HOME are defined
./test_go.sh: line 28: /var/tmp/go-test: No such file or directory

go build needs HOME/GOCACHE to locate its build cache; without it the binary is never produced. HOME=/root is the value tmt forwarded before 1.75.0, so this just restores prior behavior. (Seen in run 27098743377.)