virStorageBackendIQNFound: Rework iscsiadm output parsing
virStorageBackendIQNFound: Rework iscsiadm output parsing

Firstly, we can utilize virCommandSetOutputBuffer() API which
will collect the command output for us. Secondly, sscanf()-ing
through each line is easier to understand (and more robust) than
jumping over a string with strchr().

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>

eskultety/libvirt,zippy2/libvirt,libvirt/libvirt,jardasgit/libvirt,olafhering/libvirt,nertpinx/libvirt,jardasgit/libvirt,olafhering/libvirt,andreabolognani/libvirt,jardasgit/libvirt,nertpinx/libvirt,crobinso/libvirt,libvirt/libvirt,olafhering/libvirt,zippy2/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,olafhering/libvirt,crobinso/libvirt,jfehlig/libvirt,eskultety/libvirt,andreabolognani/libvirt,eskultety/libvirt,andreabolognani/libvirt,zippy2/libvirt,libvirt/libvirt,eskultety/libvirt,jfehlig/libvirt,jfehlig/libvirt,andreabolognani/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,eskultety/libvirt,zippy2/libvirt,andreabolognani/libvirt,crobinso/libvirt,nertpinx/libvirt,jardasgit/libvirt,crobinso/libvirt,jfehlig/libvirt,libvirt/libvirt,fabianfreyer/libvirt