Tobiko downloads images from their URL when their test need to upload
them to glance
In some cases this is problematic because some of those images are big
and there may be timeouts affecting the tests
With this patch, tobiko downloads the ubuntu-minimal image before the
tobiko tests are executed (during the execution of the ansible/infrared
tobiko roles), which should avoid timeouts during the test execution
The intention is to extend this patch to other images such as CentOS,
RHEL and Fedora
NOTE: this patch does not modify the tests, it just adds the role so
that the Ubuntu images are downloaded - a later patch will modify the
tests so that they stop downloading the images and find them in the
configured path instead
Change-Id: Ifff8214b7d4a3c2a78d97b171714090fd64d60dd
4ad11e3710