libvirt.test: Add some more normal/error cases about sync test

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
This exception will be caught in line 126 and FAIL the case, will not got SKIP.

```
17:58:47 ERROR| Traceback (most recent call last):
17:58:47 ERROR|   File "/home/wayne/work/virt-test/virttest/standalone_test.py", line 219, in run_once
17:58:47 ERROR|     run_func(self, params, env)
17:58:47 ERROR|   File "/home/wayne/work/virt-test/test-providers.d/downloads/io-github-autotest-libvirt/libvirt/tests/src/virsh_cmd/domain/virsh_qemu_agent_command.py", line 126, in run
17:58:47 ERROR|     raise error.TestFail(details)
17:58:47 ERROR| TestFail: Cannot execute this test for domain doesn't have pm-suspend-hybrid command!
```