Trying to run

  $ ./configure --prefix=$HOME/usr/libvirt-git
  $ make install

results in libvirt trying to install in /usr/lib/wireshark/plugins/....
with predictable amounts of fail. The configure script should not be
hardcoding /usr/lib by default but rather honour $libdir
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>