samba: wait for smbd process to exit

samba: wait for smbd process to exit

I saw

2013-08-03T12:56:26.641 DEBUG:teuthology.orchestra.run:Running [10.214.131.28]: 'sudo killall -9 smbd'
2013-08-03T12:56:26.727 DEBUG:teuthology.orchestra.run:Running [10.214.131.28]: 'sudo lsof /home/ubuntu/cephtest/93695/mnt.0'
2013-08-03T12:56:26.830 INFO:teuthology.orchestra.run.out:[10.214.131.28]: COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
2013-08-03T12:56:26.830 INFO:teuthology.orchestra.run.out:[10.214.131.28]: smbd    12381 root  cwd    DIR    0,0        0    1 /home/ubuntu/cephtest/93695/mnt.0

which makes me think we just need to wait a moment before
attempting the umount?

Signed-off-by: Sage Weil <sage@inktank.com>