feat(instances): grow a disk while the VM runs or is paused

The resize tab enabled disk growth only for a shut-off VM, although
resize_disk already grows a running domain's disk through blockResize.
The button is now enabled for running and paused VMs too. A live test
grows qcow2 and raw disks of a running and of a paused VM and checks the
size the guest sees, the volume size, the unchanged persistent definition
and the state.

README.md

@@ -533,6 +533,7 @@ A rollback leaves the clone on a detached HEAD at the restored commit; the updat
 - A template VM is changed or deleted only by superusers and staff owners with the matching permission; other owners can still view, open the console and clone it. Power cycle no longer starts a template.
 - A VM that vanishes from its compute keeps its owners for `INSTANCE_OWNERSHIP_RETENTION_DAYS` (30) in case the same UUID comes back; superusers list and remove these records on the "Removed VMs" admin page.
 - The log rotates (10 MB × 5) in `data/webvirtcloud.log`.
+- A disk can be grown while its VM runs or is paused, not only when it is shut off.
 - gstfsd finds the guest's operating system the way libguestfs inspects it, so a root on LVM works, and it always answers (an error when it finds no or several operating systems). Update `/usr/local/bin/gstfsd` on every compute (see [Adding a Compute Node](#adding-a-compute-node), step 3).
 - Docker no longer publishes port 6080; the console goes through nginx on the panel's port (`WS_PUBLIC_PORT`, default 80).