Fix state sync logic related to the PAUSED VM state

A VM may get into the paused state not only because the user request
via API calls, but also due to (temporary) external instrumentations.
Before the virt layer can reliably report the reason, we simply ignore
the state discrepancy. In many cases, the VM state will go back to
running after the external instrumentation is done.

Fix bug 1097806.

Change-Id: I8edef45d60fa79d6ddebf7d0438042a7b3986b55
Refactor: extract method: driver_dict_from_config

Related to blueprint xenapi-volume-drivers

Extract method to create driver registries, so that it could be re-used
in xenapi for a similar purpose.

Change-Id: Ifd25d12335ac96a15dfea4c5ab7f315ff7ddfd8b
Merge "Fix state sync logic related to the PAUSED VM state"
Merge "Refactor: extract method: driver_dict_from_config"