libvirt-tests: rebuild the struct of dir libvirt/tests.

Make a dir struct for libvirt-tests. Referring to "virsh help",
the virsh_cmd module contains 11 parts. The outline looks
like:

libvirt/tests/                              virsh_cmd/
            |---cfg/                            |---domain/
                |---kernel_panic.cfg            |---monitor/
                |---remove_guest.cfg            |---host/
                |---virsh_cmd/                  |---interface/
            |---src/                            |---filter/
                |---kernel_panic.py             |---network/
                |---remove_guest.py             |---nodedev/
                |---virsh_cmd/                  |---secret/
                                                |---snapshot/
                                                |---pool/
                                                |---volume/

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