qemu: use virBuffer in qemuBuildSCSIiSCSIHostdevDrvStr
qemu: use virBuffer in qemuBuildSCSIiSCSIHostdevDrvStr

Instead of source to enable use of virBuffer functions in
string construction.

Signed-off-by: Anya Harter <3b600d71e871b87e4f6db998f686f2f91c50d260@redhat.com>

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