Currently, if we try to stop or start a network two time in a row, the
second call will fail. With this patch:
- we don't recreate a network, if it exists
- we only stop a network if it's active, and so we avoid an exception
saying the network is not active
* test: mock libvirt
* add integration tests for virt_net
* test: enable virt_net test on RedHat 7 and 8
* ci: use the unsupported alias
* tests that require privileged mode are run in VM
* virt_net/create raise unexpected libvirt exception
* import mock from units.compat
* virt_net: do not call create() on "active" network
* virt_net func test: only clean up the libvirt packages
* test: virt_net: don't use assert_called()
* virt_net: add the destructive alias
* move the test in virt_net dir
* test/virt_net: clean up the network at the end
