fix(interfaces): interface changes roll back as one, a running one is not deleted, each interface is read once

Plan reviewed with Codex; tried on a udev host (AlmaLinux 10) and a
netcf one (AlmaLinux 8).

- Changes are one change of the host's configuration (libvirt's
  interface change transaction): a bridge that does not start used to
  be undefined, leaving its member without the addresses and start
  mode the bridge took from it; now the whole change rolls back, the
  member's own configuration too, and so does a commit libvirt refuses.
  A rollback that fails too is reported with the failure, saying the
  host's configuration may be changed.
  Deleting a bridge, which defines its
  members again on their own, is one change as well.
- A running interface is not deleted: the page hid Delete, but a post
  deleted it. A bridge with addresses and several members is refused
  (which member takes the addresses is the user's choice); the
  confirmation says that its members are defined again.
- A bridge takes only a device in no bridge, bond or VLAN as the host
  has them configured, at any depth (a bridge's bond's devices), not
  the loopback, a libvirt network's bridge or a VM's tap; an ethernet
  interface configures only such a device too.
- Whether the host can change interfaces: unsupported or refused by
  its access rules is a no, bad XML a yes, anything else (the
  connection, the login) is raised instead of taken for a yes. A page
  whose host could not be read offers no actions.
- Reads: the list reads each interface's XML once from one listing
  (listAllInterfaces: every state, not the active and the defined ones
  apart); a page reads the running and the saved definition once each
  (cached_property). netcf writes a link speed of -1 for a card that
  has none (a virtio one) and then refuses its own XML: the saved one
  is read instead, where virsh and the page failed. Name and MAC come
  from libvirt's object, without a call. Each family says how it is
  addressed (DHCP, autoconf, static or none) and every address, its
  prefix where it has one; no
  address is not "DHCP" any more. A bridge's members carry their link
  state and speed; an unknown speed (0, -1, 4294967295) is none.
- The interface API lists from the same reader. get_details,
  get_bridge, get_bridge_slave_ifaces and the per-family getters go.

vrtManager/connection.py

@@ -558,15 +558,8 @@ class wvmConnect(object):
         return virtnet
 
     def get_ifaces(self):
-        """
-        :return: list of host interfaces
-        """
-        interface = []
-        for inface in self.wvm.listInterfaces():
-            interface.append(inface)
-        for inface in self.wvm.listDefinedInterfaces():
-            interface.append(inface)
-        return interface
+        """The names of the host's interfaces, in every state."""
+        return [iface.name() for iface in self.wvm.listAllInterfaces(0)]
 
     def get_nwfilters(self):
         """
@@ -1052,14 +1045,19 @@ class wvmConnect(object):
         return instance
 
     def can_change_interfaces(self):
-        """False when the host's libvirt cannot define interfaces (the udev
-        backend only reads them). The definition sent is invalid, so nothing is
-        defined: a backend without define refuses it with VIR_ERR_NO_SUPPORT,
-        one with define with an XML error."""
+        """Whether the host's libvirt can define interfaces: the udev backend
+        only reads them. The definition sent is invalid, so nothing is
+        defined: a backend without define refuses it as unsupported, one with
+        define as bad XML. Any other refusal, of the connection say, is not an
+        answer and is raised; one the host's access rules give is a no."""
         try:
             self.wvm.interfaceDefineXML("<interface/>", 0)
         except libvirtError as err:
-            return err.get_error_code() != libvirt.VIR_ERR_NO_SUPPORT
+            if err.get_error_code() in (libvirt.VIR_ERR_NO_SUPPORT, libvirt.VIR_ERR_OPERATION_DENIED):
+                return False
+            if err.get_error_code() in (libvirt.VIR_ERR_XML_ERROR, libvirt.VIR_ERR_XML_DETAIL):
+                return True
+            raise
         return True
 
     def get_net_devices(self):