spec: default vbox according to libvirtd build

Commit ba5f3c7c moved virtualBox support into libvirtd, but the spec
file was still unconditionally requesting it even when not building
the server side.  Thankfully there were no ill effects for a
client_only build, as most uses of %{with_vbox} were guarded by
%{with_libvirtd}; but we might as well avoid confusion by more
closely matching the makefile.

* libvirt.spec.in (with_vbox): Hoist to server conditionals.
Signed-off-by: NEric Blake <eblake@redhat.com>

libvirt.spec.in

@@ -50,6 +50,7 @@
 %define with_lxc           0%{!?_without_lxc:%{server_drivers}}
 %define with_uml           0%{!?_without_uml:%{server_drivers}}
 %define with_libxl         0%{!?_without_libxl:%{server_drivers}}
+%define with_vbox          0%{!?_without_vbox:%{server_drivers}}
 
 %define with_qemu_tcg      %{with_qemu}
 # Change if we ever provide qemu-kvm binaries on non-x86 hosts
@@ -71,7 +72,6 @@
 
 # Then the hypervisor drivers that run outside libvirtd, in libvirt.so
 %define with_openvz        0%{!?_without_openvz:1}
-%define with_vbox          0%{!?_without_vbox:1}
 %define with_vmware        0%{!?_without_vmware:1}
 %define with_phyp          0%{!?_without_phyp:1}
 %define with_esx           0%{!?_without_esx:1}