qemu-tool: Stub out qemu-timer functions

qemu-tool: Stub out qemu-timer functions

Block drivers may use timers for flushing metadata to disk or
reconnecting to a network drive.  Stub out the following functions in
qemu-tool.c:

QEMUTimer *qemu_new_timer_ns(QEMUClock *clock, int scale,
                             QEMUTimerCB *cb, void *opaque)
void qemu_free_timer(QEMUTimer *ts)
void qemu_del_timer(QEMUTimer *ts)
void qemu_mod_timer(QEMUTimer *ts, int64_t expire_time)
int64_t qemu_get_clock_ns(QEMUClock *clock)

They will result in timers never firing when linked against qemu-tool.o.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>