[CORE] vmm_manager: Improve use of locks in guest create and destroy

The vmm_manager_guest_create() and vmm_manager_guest_destroy() APIs
depend upon vmm_guest_apace_xxx() APIs which in-turn use sleepable
locks hence we should not call vmm_guest_aspace_xxx() APIs with
"mngr.lock" spinlock held.

This patch fixes above described use of "mngr.lock" in guest create
and destroy APIs.

Signed-off-by: Anup Patel <anup@brainfault.org>