storage: Fix existing parent check for vHBA creation

storage: Fix existing parent check for vHBA creation

https://bugzilla.redhat.com/show_bug.cgi?id=1472277

Commit id '106930aaa' altered the order of checking for an existing
vHBA (e.g something created via nodedev-create functionality outside
of the storage pool logic) which inadvertantly broke the code to
decide whether to alter/force the fchost->managed field to be 'yes'
because the storage pool will be managing the created vHBA in order
to ensure when the storage pool is destroyed that the vHBA is also
destroyed.

This patch moves the check (and checkParent helper) for an existing
vHBA back into the createVport in storage_backend_scsi. It also
adjusts the checkParent logic to more closely follow the intentions
prior to commit id '79ab0935'. The changes made by commit id '08c0ea16f'
are only necessary to run the virStoragePoolFCRefreshThread when
a vHBA was really created because there's a timing lag such that
the refreshPool call made after a startPool from storagePoolCreate*
wouldn't necessarily find LUNs, but the thread would. For an already
existing vHBA, using the thread is unnecessary since the vHBA already
exists and the lag to configure the LUNs wouldn't exist.

Signed-off-by: John Ferlan <jferlan@redhat.com>