In cases when hosting subscription is shared by many computer partitions,
which belongs to different computers all computers from this group need access
to this hosting subscription.

Implement destroy_requested state and transition and mark as soon as possible
this state in case when software instance is being destroyed. In
SalePackingList_requestStoredSoftwareInstanceState support destroy_requested,
which in case of ongoing destruction is no-op.

In such scenario no hosting packing lists shall be created.

When instance has packing list related with setup and cleanup and both are,
confirmed state in case of typical scenario (node says stopped and just after
destroyed) its automatically created instance hosting sale packing lists shall
be delivered.

Do not call checkConnected, in order to have only checkCyclic fired up.

Thanks to this it is possible to manipulate not finished (not delivered yet)
packing lists during destruction process.

vifib_base does not have this portal type, it exists only at vifib_open_trade.

software_instance was not available anymore.

During finding root software instance not full tree is analysed. In order to
have more complete graph just add some nodes which shall be. They will be
mostly leaf nodes, so they do not impact graph connectivity nor cycleism.

Root software instance requests shall be disallowed, period.

Graphs were not cyclic.

Moreover update existing tests in order to simulate real cases.

Even more -- return True in case if all was ok.

Instead of raising ValueError, which is used all the time, except
DisconnectedSoftwareTree exception.

It allows to have selective detection of software instance problem and allows
to test what exactly was told.

Treat tree of software instance as graph and simulate requested changes.
Before doing any real changes check if graph is still connected.

Add utility method to software instance class in order to use collections
module and have fast graph walking.

success