python: add API exports for virConnectListAllDomains()

python: add API exports for virConnectListAllDomains()

This patch adds export of the new API function
virConnectListAllDomains() to the libvirt-python bindings. The
virConnect object now has method "listAllDomains" that takes only the
flags parameter and returns a python list of virDomain object
corresponding to virDomainPtrs returned by the underlying api.

The implementation is done manually as the generator does not support
wrapping list of virDomainPtrs into virDomain objects.