Merge pull request #23 from tomasdubec/PCI-2046

FEATURE: PCI-2046 RAM/CPU overcommit per compute node
Merge pull request #25 from tomasdubec/PCI-2025

BUGFIX: PCI-2025 delete domain after unsuccessful instance spawn

after much discussion, it had to be done this way with "finally". Somehow self.destroy clears the exception stack and simple "raise" would produce an error.