qemu: command: Inject password-secret only when not using JSON props

The 'file.password-secret' injection should be used only if we are using
the old formatter. When formatting the source string from the JSON
properties, the property should be added there.

Also drop the comment which refers to stuff that will not be used in
libvirt since -blockdev is the way to go.

src/qemu/qemu_command.c

@@ -1578,6 +1578,9 @@ qemuBuildDriveSourceStr(virDomainDiskDefPtr disk,
         }
 
         virQEMUBuildBufferEscapeComma(buf, source);
+
+        if (secinfo && secinfo->type == VIR_DOMAIN_SECRET_INFO_TYPE_AES)
+            virBufferAsprintf(buf, ",file.password-secret=%s", secinfo->s.aes.alias);
     } else {
         if (!(source = virQEMUBuildDriveCommandlineFromJSON(srcprops)))
             goto cleanup;
@@ -1592,16 +1595,6 @@ qemuBuildDriveSourceStr(virDomainDiskDefPtr disk,
             virBufferAsprintf(buf, "file.debug=%d,", cfg->glusterDebugLevel);
     }
 
-    if (secinfo && secinfo->type == VIR_DOMAIN_SECRET_INFO_TYPE_AES) {
-        /* NB: If libvirt starts using the more modern option based
-         *     syntax to build the command line (e.g., "-drive driver=rbd,
-         *     filename=%s,...") instead of the legacy model (e.g."-drive
-         *     file=%s,..."), then the "file." prefix can be removed
-         */
-        virBufferAsprintf(buf, "file.password-secret=%s,",
-                          secinfo->s.aes.alias);
-    }
-
     if (encinfo)
         virQEMUBuildLuksOpts(buf, &disk->src->encryption->encinfo,
                              encinfo->s.aes.alias);