Library /lib/libnss_mysql.so.2.0.0 depends on /usr/lib/libmysqlclient.so.12. Binaries and libraries on the root filesystem basically should not depend on /usr. However, I don't see any good solution for this particular issue offhand.
$ ldd /usr/lib/libnss_mysql.so linux-gate.so.1 => (0xffffe000) libmysqlclient.so.15 => /usr/lib/libmysqlclient.so.15 (0xb7d95000) Поскольку сейчас libnss лежит тоже в /usr/lib, предлагаю багу закрыть.