test/libcephfs/test.cc: free cmount structure before return

call ceph_shutdown to free cmount structure before return

Signed-off-by: Xing Lin <xinglin@cs.utah.edu>
Merge pull request #1782 from xinglin/coverity-fixes

test/libcephfs/test.cc: free cmount structure before return

Reviewed-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>