backend: change the order of config files to include.

In tests-shared.cfg, we will include the other config files. And
we should keep the user configuration at the last in the file list
to make the configuration from user override the default configuration.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
libvirt_vm: Override wait_for_login() method in libvirt_vm.

Override the wait_for_login method of virt_vm to support other
guest in libvirt.

If connect_uri is lxc related, we call wait_for_serial_login()
directly, without attampting login it via network.

Other connect_uri, call virt_vm.wait_for_login().

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
env_process: Set two environment variable for current connect_uri.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
utils_env: Add a suffix for vm in env.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
utils_env: Return uri specificed vms in get_all_vms().

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
libvirt_vm: make normalize_connect_uri return exact uri rather than None when input is default.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
libvirt_vm: Fix for vm.connect_uri when it is default.

Default is not always qemu.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
libvirt_vm: send ^] to serial_console when vm is lxc to close console.

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