API/create: move locking inside worker

API/create: move locking inside worker

Move the locking inside worker, so that the process doing the actual
work (create or restore) holds the lock, and can call functions which
do locking without deadlocking.

This mirrors the behaviour we use for containers, and allows to add
an 'autostart' parameter which starts the VM after successful
creation. vm_start needs the lock and as not the worker but it's
parents held it, it couldn't know that it was actually save to
continue...

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>