Use local socket for mysql client connection

This affects mysql client as well as mysqladmin, which is used in status
checks in the init script. It is important that the init script can
succeed regardless of LB state. (Prior to this commit, LB IP was used as
the host to connect to).

Related: #413
Merge pull request #414 from hughsaunders/use_local_socket_in_client_my_conf

Use local socket for mysql client connection