[WIP] AGENT: Fix releaseImageMirror formatting

When the image is of the form:

    quay.io/openshift-release-dev/ocp-release@sha256:300bce8246cf880e792e106607925de0a404484637627edf5f517375517d54a4

Splitting by ':' means that the extracted location will be:

    quay.io/openshift-release-dev/ocp-release@sha256:

Instead of

    quay.io/openshift-release-dev/ocp-release

Whereas in registries.conf we'd have the location be:

    [[registry]]
      location = "quay.io/openshift-release-dev/ocp-release"

Thus. There wouldn't be a match and the release image will be empty in
places like:

    /usr/local/share/assisted-service/assisted-service.env

or

    /etc/systemd/system/create-cluster-and-infraenv.service

Signed-off-by: Antoni Segura Puimedon <antoni@redhat.com>

pkg/asset/agent/image/ignition.go

@@ -6,6 +6,7 @@ import (
 	"net/url"
 	"path"
 	"path/filepath"
+	"regexp"
 	"strings"
 
 	"github.com/coreos/ignition/v2/config/util"
@@ -141,11 +142,16 @@ func (a *Ignition) Generate(dependencies asset.Parents) error {
 
 	// Get the mirror for release image
 	releaseImageMirror := ""
-	source := strings.Split(agentManifests.ClusterImageSet.Spec.ReleaseImage, ":")
+	source := regexp.MustCompile(`^(.+?)(@sha256)?:(.+)`).FindStringSubmatch(agentManifests.ClusterImageSet.Spec.ReleaseImage)
 	for _, config := range registriesConfig.MirrorConfig {
-		if config.Location == source[0] {
+		if config.Location == source[1] {
 			// include the tag with the build release image
-			releaseImageMirror = fmt.Sprintf("%s:%s", config.Mirror, source[1])
+			if len(source) == 4 {
+				// Has Sha256
+				releaseImageMirror = fmt.Sprintf("%s%s:%s\n", config.Mirror, source[2], source[3])
+			} else if len(source) == 3 {
+				releaseImageMirror = fmt.Sprintf("%s:%s\n", config.Mirror, source[2])
+			}
 		}
 	}