engine,userportal,webadmin:Remove ACTION_TYPE_FAILED_VM_NOT_EXIST

Prior to this change 2 almost identical messages exist in the code:
* ACTION_TYPE_FAILED_VM_NOT_FOUND
* ACTION_TYPE_FAILED_VM_NOT_EXIST
The change replaces all usages of ACTION_TYPE_FAILED_VM_NOT_EXIST with
ACTION_TYPE_FAILED_VM_NOT_FOUND and removes the definition of the first.

Change-Id: Ib3204225b8cdc870b0292aeb8c71af4c8f13ff10
Signed-off-by: Yevgeny Zaspitsky <yzaspits@redhat.com>