So we unify parsing and building the XML.
Since we already do this for vmmDomain, take the opportunity to move
the shared infrastructure into vmmLibvirtObject
Basically, drop usage of nested main loops. As has been documented in
other commit messages, we use nested main loops in ways they aren't
supposed to be used. They gave us async behavior that would block
callers, but had weird behavior in some edge cases.
Switch to having async dialogs be 100% async, requiring the user to
pass in a completion callback which is triggered after the async
action is complete.
This adds initial UI for managing snapshots: list, run/revert, delete,
add, and redefining (for changing <description>) supported, but currently
only for internal snapshots. The UI is mostly in its final form except for
some bells and whistles.
The real remaining question is what do we want to advertise and support.
Internal (qcow2) snapshots are by far the simplest to manage, very
mature, and already have the semantics we want.
However most recent libvirt and qemu work has been to facilitate
external snapshots, which are more extensible and can be performed
live, and with qemu-ga coordination for extra safety. However
they make things much harder for virt-manager at the moment.
Until we have a plan, this work should be considered experimental
and not be relied upon.
