virttest: Add utils_conn module into virttest.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
Add test for virsh connect.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
Some fix for utils_conn and utils_libvirtd

(1).use data_dir module to get a tmp_dir.
(2).remove some error classes seems unnessary,
    to reuse code as possible.
(3).remove some unused variables.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>