libcephfs:  Fix shutdown segfault

client->shutdown() should only be called once, but with
new inited flag, we were calling it twice.  This sets
the inited flag back to false after client->shutdown()
is called the first time.

Broken by 133295ed001a950e3296f4e88a916ab2405be0cc.

Signed-off-by: Sam Lang <sam.lang@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>