Artefact last modified is returned my DMF auth call (#600)

* Last modified is stored as part of artifact and returns accordingly by
APIs.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Fixed tests.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Check value > 0

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Use created at.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Sonar issue fixed.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

hawkbit-repository/hawkbit-repository-jpa/src/test/java/org/eclipse/hawkbit/repository/jpa/DeploymentManagementTest.java

@@ -458,7 +458,7 @@ public class DeploymentManagementTest extends AbstractJpaIntegrationTest {
                 .as("TargetUpdateStatus IN_SYNC")
                 .allMatch(target -> TargetUpdateStatus.IN_SYNC.equals(target.getUpdateStatus()))
                 .as("InstallationDate equal to LastModifiedAt")
-                .allMatch(target -> target.getLastModifiedAt().equals(target.getInstallationDate()));
+                .allMatch(target -> target.getLastModifiedAt() == target.getInstallationDate());
     }
 
     @Test