To allow for fault injection of the virCommand dry run,
add the ability to register a callback. The callback will
be passed the argv, env and stdin buffer and is expected
to return the exit status and optionally fill stdout and
stderr buffers.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

So far it's just virCommandSetDryRun.

And while doing this, fix one error raised by coverity. With
current code, @actual_cmd is allowed to be NULL for the whole
run of testVirNetDevBandwidthSet. However, if something else
was expected, the @actal_cmd is passed to virtTestDifference
which dereference it immediately.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

On openSuse, (and possibly other distros), tc isn't located in
/sbin/tc. To get rid of that problem, use TC constant instead of hard
coded /sbin/tc in the expected string

This reverts commit 2996e6be
and some parts of 2636dc8c.

The former one tried to implement QoS setting on bridgeless networks.
However, as discussed upstream [1], the patch is far away from being
useful in even a single case. The whole idea of network QoS is to have
aggregated limits over several interfaces. This patch is doing
completely the opposite when merging two QoS settings (from the network
and the domain interface) into one which is then set at the domain
interface itself, not the network.

The latter one is the test for the previous one. Now none of them makes
sense.

1: https://www.redhat.com/archives/libvir-list/2014-January/msg01441.html

Conflicts:
	tests/virnetdevbandwidthtest.c: New test has been introduced since
    then.

The test tries to set some QoS limits and check if the commands
that are actually executed are the expected ones.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

The only API tested so far would be virNetDevBandwidthMinimal.
But there's more to come!
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>