Add logs about which images are being pulled

[jlausuch]

It would be very useful to include the tested/pulled container images in the logs.

Current logs, like bci_test-result.xml, only contain info about the results with the name of the container, e.g.:

<?xml version="1.0" encoding="utf-8"?>
<testsuites>
  <testsuite errors="0" failures="0" hostname="install" name="minimal" skipped="1" tests="6" time="10.771" timestamp="2022-05-02T09:57:48.688025">
    <testcase classname="tests.test_minimal" name="test_minimal_image_size[container1-size1]" time="3.766"/>
    <testcase classname="tests.test_minimal" name="test_minimal_image_size[container0-size0]" time="3.802">
      <skipped message="Temporary size increase due to mozilla cert bundle hack" type="pytest.xfail"/>
    </testcase>
    <testcase classname="tests.test_minimal" name="test_fat_packages_absent[auto_container1]" time="3.145"/>
    <testcase classname="tests.test_minimal" name="test_fat_packages_absent[auto_container0]" time="3.379"/>
    <testcase classname="tests.test_minimal" name="test_rpm_absent_in_micro[container0]" time="2.698"/>
    <testcase classname="tests.test_minimal" name="test_rpm_present_in_micro[container0]" time="2.656"/>
  </testsuite>
</testsuites>

Maybe we could inject it here:

<testcase classname="tests.test_minimal" name="test_fat_packages_absent[auto_container1]" image="registry.suse.de/xyz" time="3.145"/>

or just create a log message saying "pulling image registry.suse.de/xyz"..