domiftune: Adjust max value

Turns out this test made an assumption that the value being passed to
libvirt for the 'domiftune' as the maximum was in bytes per second rather
than the libvirt expected kilobytes per second.

The reality is, libvirt's documentation wasn't very clear so that has
been fixed. Furthermore, there was a bug in the /sbin/tc code which was
fixed that resulted in libvirt actually failing (correctly) when such a
large and incorrect value was passed. For details read the upstream commit:

http://www.redhat.com/archives/libvir-list/2014-February/msg00904.html

NOTE:
It's now not even possible to get the "maximum" bytes per second passed,
but we can come close (within 295 bytes) by passing a kilobytes value.

Signed-off-by: John Ferlan <jferlan@redhat.com>
domiftune: Update test to handle clearing inbound/outbound

In libvirt 1.2.3, commit id '14973382' it will now be possible to pass
a zero (0) as an inbound or outbound parameter to domiftune in order to
clear all the settings found.

Thus, modify the cfg to move the setting of input/output to zero from
negative to positive testing.  Also set a marker that will allow the
test code to handle the attempted clear.

Since previously 0 was considered an error, the code was modified to
check the libvirt version and handle the results based upon the version.
Prior to libvirt 1.2.3, a zero in a positive test would cause a failure,
but since it's known that way just adjust the expected results.

For the new code, we'll set the variables average, peak, and burst to
values and then pass the zero along to ensure that each of the values
was cleared on the next check.  This is only done of course if we are
at libvirt 1.2.3 or later.

NOTE:
I tested the results for the "now" good case. I also built a libvirt prior
to the specific commit id and tested that if a zero was passed, then the
code would follow the path of the expected failure. As part of this same
build - I also tested the error path if the new code changes or fails
to clear the other fields, then emit a failure.

Signed-off-by: John Ferlan <jferlan@redhat.com>
Merge pull request #108 from jferlan/domiftune

Domiftune changes