Adapt tests to new test_distro

The new test_distro's manifest produces a slightly different empty
manifest when serialized even without content.  Cloud API and Koji tests
have been adapted to match.

Weldr tests have been updated in several ways:
- The test_distro content resolver is used to resolve manifest content
  before serializing.
- The test scenarios in TestCompose have been named for easier
  troubleshooting (easier to identify a failing test by name).
- Manifests that work with the secondary ostree repo (the "other") use
  the appropriate URL and ref and create a secondary "other" serialized
  manifest.

The weldr API's test flag for resolving ostree commits does not produce
the same, fixed hash every time but instead computes a sha256 from the
URL + ref, like we do in the test manifests.

internal/cloudapi/v2/v2_koji_test.go

@@ -323,6 +323,8 @@ func TestKojiCompose(t *testing.T) {
 		},
 	}
 
+	emptyManifest := `{"version":"2","pipelines":[{"name":"build"},{"name":"os"}],"sources":{"org.osbuild.curl":{"items":{"":{"url":""}}}}}`
+	expectedManifests := `{"manifests":[` + emptyManifest + `,` + emptyManifest + `],"kind":"ComposeManifests"}`
 	for idx, c := range cases {
 		name, version, release := "foo", "1", "2"
 		t.Run(fmt.Sprintf("Test case #%d", idx), func(t *testing.T) {
@@ -459,7 +461,7 @@ func TestKojiCompose(t *testing.T) {
 			test.TestRoute(t, handler, false, "GET", fmt.Sprintf("/api/image-builder-composer/v2/composes/%v", finalizeID), ``, http.StatusOK, c.composeStatus, `href`, `id`)
 
 			// get the manifests
-			test.TestRoute(t, handler, false, "GET", fmt.Sprintf("/api/image-builder-composer/v2/composes/%v/manifests", finalizeID), ``, http.StatusOK, `{"manifests":[{"version":"2","pipelines":[],"sources":{}},{"version":"2","pipelines":[],"sources":{}}],"kind":"ComposeManifests"}`, `href`, `id`)
+			test.TestRoute(t, handler, false, "GET", fmt.Sprintf("/api/image-builder-composer/v2/composes/%v/manifests", finalizeID), ``, http.StatusOK, expectedManifests, `href`, `id`)
 
 			// get the logs
 			test.TestRoute(t, handler, false, "GET", fmt.Sprintf("/api/image-builder-composer/v2/composes/%v/logs", finalizeID), ``, http.StatusOK, `{"kind":"ComposeLogs"}`, `koji`, `image_builds`, `href`, `id`)