Addresses review comments, specifically:
* updates qvm-clone tests to handle ignore_errors option
* adds manpage reference to new --ignore-errors option
* trims line length in qvm-clone changes
All tests should now be passing, including the new qvm-clone
functionality.
This way we don't need separate admin.vm.Clone call, which is tricky to
handler properly with policy.
A VM may not have access to all the properties and other metadata, so
add ignore_errors argument, for best-effort approach (copy what is
possible). In any case, failure of cloning VM data fails the whole
operation.
When operation fails, VM is removed.
While at it, allow to specify alternative VM class - this allows
morphing one VM into another (for example AppVM -> StandaloneVM).
Adjust qvm-clone tool and tests accordingly.
QubesOS/qubes-issues#2622
