CIMI: expose import and export of systems and system templates

for drivers that support these operations

I've made changes to mock driver and its yaml files to allow you to try it out.
Looking for some advice in how to proceed:
- push as-is if you're okay with the changes
- push without the mock related changes
- "implement" the mock import/export operations:
-- with a different message or NOP
-- import could cause a new machine with a name or description based on the ovf source name be created (without actually reading from the source)
-- import could try to read the ovf file and create a machine with a name based on the <VirtualSystem>'s <name> value (picking hard-coded defaults for the other attributes to keep it a mock).
?