ceph: fix shutdown race

ceph: fix shutdown race

Shut down MonClient before messenger, to avoid race with MonClient::tick()
and MonClient::shutdown().

Fixes

#0  __lll_lock_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:136
#1  0x00007f44475e2849 in _L_lock_953 () from /lib/libpthread.so.0
#2  0x00007f44475e266b in __pthread_mutex_lock (mutex=0x14d8dc8) at pthread_mutex_lock.c:61
#3  0x00000000005ae090 in Mutex::Lock (this=0x14d8db8, no_lockdep=false) at ./common/Mutex.h:108
#4  0x000000000068440e in MonClient::shutdown (this=0x14d8c30) at mon/MonClient.cc:386
#5  0x00000000005b2653 in ceph_tool_common_shutdown (ctx=0x14d84c0) at tools/common.cc:661
#6  0x00000000005ada29 in main (argc=7, argv=0x7fff8a2394c8) at tools/ceph.cc:304

vs

#0  0x00007f44475e8a0b in raise (sig=<value optimized out>) at ../nptl/sysdeps/unix/sysv/linux/pt-raise.c:42
#1  0x00000000005eff6b in reraise_fatal (signum=11) at global/signal_handler.cc:59
#2  0x00000000005f0165 in handle_fatal_signal (signum=11) at global/signal_handler.cc:106
#3  <signal handler called>
#4  0x0000000000000000 in ?? ()
#5  0x000000000068661a in MonClient::tick (this=0x14d8c30) at mon/MonClient.cc:621
#6  0x0000000000689e3b in MonClient::C_Tick::finish(int) ()
#7  0x000000000061b3c5 in SafeTimer::timer_thread (this=0x14d8df8) at common/Timer.cc:102
#8  0x000000000061c6f0 in SafeTimerThread::entry() ()
#9  0x00000000005f1219 in Thread::_entry_func (arg=0x14e1a00) at common/Thread.cc:41
#10 0x00007f44475e0971 in start_thread (arg=<value optimized out>) at pthread_create.c:304
#11 0x00007f4445ead92d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:112
#12 0x0000000000000000 in ?? ()

Signed-off-by: Sage Weil <sage@newdream.net>