librados-config.cc: catch ceph::FailedAssertion exception

CID 717157 (#1-2): Uncaught exception (UNCAUGHT_EXCEPT)
 root_function: In function main(int, char const **) an exception
 of type ceph::FailedAssertion is thrown and never caught.

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