The only useful translation of "%s" as a format string is "%s" (I
suppose you could claim "%1$s" is also valid, but why bother).  So
it is not worth translating; fixing this exposes some instances
where we were failing to translate real error messages.  This makes
the fix of commit 097da1ab more generic, as well as ensuring no
future regressions.

* cfg.mk (sc_prohibit_useless_translation): New rule.
* src/lxc/lxc_driver.c (lxcSetVcpuBWLive): Fix offender.
* src/openvz/openvz_conf.c (openvzReadFSConf): Likewise.
* src/qemu/qemu_cgroup.c (qemuSetupCgroupForVcpu): Likewise.
* src/qemu/qemu_driver.c (qemuSetVcpusBWLive): Likewise.
* src/xenapi/xenapi_utils.c (xenapiSessionErrorHandle): Likewise.