domtime: update for s390x

[smitterl]

hwclock is not available on s390x and guest agent operators that modify the time either.

1. Don't try to restore time (with --now flag) during teardown.
2. Disable test cases that try to modify time.
3. Skip step that uses hwclock.

[smitterl]

JOB ID     : c2abf4ec26995daa203755684f49cb314dc88c4f
JOB LOG    : /var/log/avocado/job-results/job-2024-10-09T13.11-c2abf4e/job.log
 (1/8) type_specific.io-github-autotest-libvirt.virsh.domtime.positive.get_time:  PASS (21.59 s)
 (2/8) type_specific.io-github-autotest-libvirt.virsh.domtime.positive.with_pretty:  PASS (22.58 s)
 (3/8) type_specific.io-github-autotest-libvirt.virsh.domtime.positive.suspend_vm:  PASS (32.88 s)
 (4/8) type_specific.io-github-autotest-libvirt.virsh.domtime.positive.managedsave_vm:  PASS (50.37 s)
 (5/8) type_specific.io-github-autotest-libvirt.virsh.domtime.negative.shutdown_vm:  PASS (31.83 s)
 (6/8) type_specific.io-github-autotest-libvirt.virsh.domtime.negative.no_agent_channel:  PASS (23.68 s)
 (7/8) type_specific.io-github-autotest-libvirt.virsh.domtime.negative.no_agent:  PASS (22.31 s)
 (8/8) type_specific.io-github-autotest-libvirt.virsh.domtime.negative.readonly_test.get_time_readonly:  PASS (22.74 s)
RESULTS    : PASS 8 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 | CANCEL 0
JOB HTML   : /var/log/avocado/job-results/job-2024-10-09T13.11-c2abf4e/results.html
JOB TIME   : 228.39 s