Update ruby-libvirt dependency to 0.5.0

Ruby-libvirt 0.5.0 released and  include network definition update,
which is necessary to support multi-VM/multi network support.

https://rubygems.org/gems/ruby-libvirt
update dependency ruby-libvirt 0.5.2

- ruby-libvirt released minor fixes for its 0.5 version.

Signed-off-by: Hiroshi Miura <miurahr@linux.com>
ruby-libvirt dependency update

- accept future updates on 0.5.x

Signed-off-by: Hiroshi Miura <miurahr@linux.com>
Merge branch 'update_libvirt_ver' into travis_libvirt_capability_test