do not raise an exception if we cannot increase the value.

otherwise it will be invokec by supervisord.

so that we can really have max_connections=1000 as written in mariadb.cnf.

Revert "Use specific version of setuptools because the current version(0.6c12dev_r88997) is not working" because was commited in the wrong branch

This reverts commit 99bbbf51.

with this, we can manually disable/enable a backend node so that we
can safely restart it.