Use VIR_ERR_CONFIG_UNSUPPORTED if requested security driver is disabled

There is currently no way to distinguish the case that a requested
security driver was disabled, from the case where no security driver
was available. Use VIR_ERR_CONFIG_UNSUPPORTED as the error when an
explicitly requested security driver was disabled
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/security/security_driver.c

@@ -72,6 +72,12 @@ virSecurityDriverPtr virSecurityDriverLookup(const char *name,
 
         case SECURITY_DRIVER_DISABLE:
             VIR_DEBUG("Not enabled name=%s", tmp->name);
+            if (name && STREQ(tmp->name, name)) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                               _("Security driver %s not enabled"),
+                               name);
+                return NULL;
+            }
             break;
 
         default: