Low: pgsql: PostgreSQL 9.3 compatibility for unix_socket_directories

PostgreSQL configuration parameter "unix_socket_directory" has been changed to the "unix_socket_directories" and it allows multiple socket directories in PostgreSQL 9.3 or higher.

Therefore, pgsql RA has to be changed the procedure for setting the default value of "OCF_RESKEY_socketdir" that based on "unix_socket_directory".

In PostgreSQL 9.2(or lower), if the user set "unix_socket_directory" in the postgresql.conf and does not set "OCF_RESKEY_socketdir", then pgsql RA set "OCF_RESKEY_socketdir" that based on "unix_socket_directory" automatically(It is a traditional way).

In PostgreSQL 9.3(or higher), if the user set "unix_socket_directories" in the postgresql.conf, then the user must set "OCF_RESKEY_socketdir" explicitly because pgsql RA can not detect how many directories configured in "unix_socket_directories" and which directory is used for psql command.
Merge pull request #492 from knakahira/fix-pgsql

Low: pgsql: PostgreSQL 9.3 compatibility for unix_socket_directories