[autotest] add more logging when we change DNS

In an attempt to track down why power_Idle is failing in NightlyPower,
but never for me locally or when I run it on the same machine that it
fails on in the suite, add more logging to see what's up.

BUG=5616
TEST=run power_Idle

Change-Id: I11781c83dd2939e1dc577b9ed489cfd7b7ada224

Review URL: http://codereview.chromium.org/3150025
1 file changed