conf: Add check for non scsi_host parent during vport delete

conf: Add check for non scsi_host parent during vport delete

https://bugzilla.redhat.com/show_bug.cgi?id=1420740

If the parent is not a scsi_host, then we can just happily return since
we won't be removing a vport.

Fixes a bug with the following output:

$ virsh pool-destroy host4_hba_pool
error: Failed to destroy pool host4_hba_pool
error: internal error: Invalid adapter name 'pci_0000_10_00_1' for SCSI pool

$

(cherry picked from commit 84f178bdc7ab38011cc1f76759b0a41335285a4f)