libvirt.tests: add new negative case into virsh domstate

Signed-off-by: Alex Jia <chuanchang.jia@gmail.com>
qemu_monitor_command: Add two more negative cases

Add a negative case for cover unknow cmd error, and another one
for invalid qmp command.

Signed-off-by: Wayne Sun <gsun@redhat.com>
Merge pull request #227 from chuanchang/add_cases_into_domstate

libvirt.tests: add new negative case into virsh domstate
Merge pull request #230 from waynesun09/qemu_monitor_cmd

qemu_monitor_command: Add two more negative cases
snapshot_edit: Add support to handle create snapshot without description

Add new filter case "without_desc" under disk_snapshot, update edit cmd
and snap_xml_compare function to fit the change. Update using CmdResult
according to the snapshot_current function change.

Signed-off-by: Wayne Sun <gsun@redhat.com>
snapshot_edit: Add delete_desc cases

The delete_desc cases is for delete description after snapshot created
with description. Update snap_xml_compare function for check clone and
rename cases.

Signed-off-by: Wayne Sun <gsun@redhat.com>