ceph_authtool.cc: fix implicitly-defined namespace 'std'

Fix warning from clang(++):

ceph_authtool.cc:15:17: warning: using directive refers to
 implicitly-defined namespace 'std'
using namespace std;
                ^
Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Mutex.cc: fix implicitly-defined namespace 'std'

Fix warning from clang(++):

common/Mutex.cc:14:17: warning: using directive refers to
  implicitly-defined namespace 'std'
using namespace std;
                ^

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>