Support passing QEMU lock state to dest during migration

Support passing QEMU lock state to dest during migration

Some lock managers associate state with leases, allowing a process
to temporarily release its leases, and re-acquire them later, safe
in the knowledge that no other process has acquired + released the
leases in between.

This is already used between suspend/resume operations, and must
also be used across migration. This passes the lockstate in the
migration cookie. If the lock manager uses lockstate, then it
becomes compulsory to use the migration v3 protocol to get the
cookie support.

* src/qemu/qemu_driver.c: Validate that migration v2 protocol is
  not used if lock manager needs state transfer
* src/qemu/qemu_migration.c: Transfer lock state in migration
  cookie XML