maint: avoid static zero init in drivers
    
    C guarantees that static variables are zero-initialized.  Some older
    compilers (and also gcc -fno-zero-initialized-in-bss) create larger
    binaries if you explicitly zero-initialize a static variable.
    
    * src/libxl/libxl_driver.c: Fix initialization.
    * src/lxc/lxc_controller.c: Likewise.
    * src/openvz/openvz_util.c (openvzKBPerPages): Likewise.
    * src/phyp/phyp_driver.c: Likewise.
    * src/remote/remote_driver.c: Likewise.
    * src/test/test_driver.c: Likewise.
    * src/uml/uml_driver.c: Likewise.
    * src/vbox/vbox_XPCOMCGlue.c: Likewise.
    * src/vbox/vbox_tmpl.c: Likewise.
    * src/xen/xen_driver.c: Likewise.
    * src/xen/xen_hypervisor.c: Likewise.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>