Bug 1177: Change "unix_socket_directory" paramter for PostgreSQL 9.3.

"unix_socket_directory" parameter in postgresql.conf was renamed to
"unix_socket_directories" in PostgreSQL 9.3. This patch makes db_setup
script define "unix_socket_directories" parameter to specify UNIX socket
directory when it detects PostgreSQL 9.3 or later.

Change-Id: I3dda6064eaadfc24baee87da12ab0ef8675c78f6
Signed-off-by: Shigeru Yasuda <s-yasuda@da.jp.nec.com>