Stop libvirt errors from outputting to strerr

When a libvirt error happens, the default is to output to stderr. This
behavior can be omitted by registering a new error that simply passes
without doing anything.

Resolves bug 1182184.

Change-Id: If946f9d05388c93c0630d454e5ca3b6625bb14f9
Merge "Stop libvirt errors from outputting to strerr"