Drop snapshot_create, snapshot_delete and snapshot_rollback
in favour of PVE::AbstractConfig. Qemu-specific parts are
implemented in __snapshot_XX methods in PVE::QemuConfig.
has_feature is made an implementation of the abstract
has_feature, and thus moves to PVE::QemuConfig.
Note: a new hook method needed to be introduced to be called
before creating a volume snapshot, after creating a volume
snapshot, and after unfreezing the guestfs after creating a
volume snapshot. The base method in PVE::AbstractConfig is a
noop, the implemention in PVE::QemuConfig runs the necessary
Qemu monitor commands.
Drop load_config, write_config, lock_config[_xx],
check_lock, check_protection, is_template and config_file
in favour of implementions in PVE::AbstractConfig.
Implement guest_type, __config_max_unused_disks,
config_file_lock and cfs_config_path from
PVE::AbstractConfig in PVE::QemuConfig.
