e2e: improve to have more logs

[ldevulder]

When failures occur we sometimes miss some logs.

It could be useful for some command to, for example, replace this:

err = exec.Command("virsh", "net-create", netDefaultFileName).Run()
Expect(err).To(Not(HaveOccurred()))

by this:

out, err = exec.Command("virsh", "net-create", netDefaultFileName).CombinedOutput()
Expect(err).To(Not(HaveOccurred()), out)

So in case of error we could have the output in Ginkgo logs.

Things to do:

• add some logs
• use something better to start K3s in background, because this code seems to not write k3s.log file
• use elemental-support command (see Add a elemental-support binary elemental-operator#109)

[ldevulder]

Done.