test: move image-info tests to test/

These tests (will) test more than just image-info: they'll take a
blueprint, verify that `osbuild-pipeline` generates the correct
pipeline, run osbuild with that pipeline and verify that the resulting
image has the expected image-info output.

This change only includes the latter half (i.e., only moves the already
existing tests).

Also drop python's unittest. It was hard to control output (important
for quickly spotting failures and to make travis happy). This introduces
test/run, which runs all test cases in test/cases or the ones given on
the command line.

When a failure occurs, it prints a diff of the actual and the expected
image info.

internal/blueprint/blueprint_test.go

@@ -60,7 +60,7 @@ func TestListOutputFormats(t *testing.T) {
 }
 
 func TestBlueprint_ToPipeline(t *testing.T) {
-	pipelinePath := "../../tools/test_image_info/pipelines/"
+	pipelinePath := "../../test/cases/"
 	fileInfos, err := ioutil.ReadDir(pipelinePath)
 	if err != nil {
 		t.Errorf("Could not read pipelines directory '%s': %v", pipelinePath, err)