virttest.openvswitch: remove the whitespace from the result

Whitespace character("\n") exist in the stdout data, when run
'ovs-vsctl' command in some system. better remove it before return

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
virttest.utils_net: check whether ovs is none before using it

Now when using find_current_bridge, if the host not install openvswitch
it will raise like:
AttributeError: 'NoneType' object has no attribute 'port_to_br'

This patch add a check whether ovs is exist before using it.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
virttest.qemu_vm: make test loop run correctly when using openvswitch

Currently, when close tap device, it's can not automatically cleaned
from openvswitch-db, sinece openvswitch have it's own userspace db, and
that ovsdb is considered to be only modified by the user. when
qemu exit by error, the ovs will never delete the port from it's
db, even kernel have destroied the port, as a result, when we run a
loop using ovs, it alway raise error for the port already exist.

This patch just add a workaround, make the test loop using ovs
can run normally.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
Merge pull request #1041 from humanux/ovs-work

workaround for ovs