ovsdb: Fix replication memory leak.

ovsdb: Fix replication memory leak.

Valgrind reports:

==18725== 32 bytes in 1 blocks are definitely lost in loss record 339 of 497
==18725==    at 0x4C29BBE: malloc (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==18725==    by 0x450F1F: xmalloc (util.c:112)
==18725==    by 0x41748E: replication_add_local_db (replication.c:137)
==18725==    by 0x40803B: ovsdb_replication_init (ovsdb-server.c:146)
==18725==    by 0x407C9E: ovsdb_server_connect_active_ovsdb_server
(ovsdb-server.c:1165)
==18725==    by 0x450AB3: process_command (unixctl.c:313)
==18725==    by 0x4500DC: run_connection (unixctl.c:347)
==18725==    by 0x44FFB6: unixctl_server_run (unixctl.c:400)
==18725==    by 0x4081AC: main_loop (ovsdb-server.c:182)
==18725==    by 0x406432: main (ovsdb-server.c:429)

Fixes: 60e0cd041958 ("ovsdb: Replication usability improvements")
Signed-off-by: Joe Stringer <joe@ovn.org>
Acked-by: Flavio Fernandes <flavio@flaviof.com>
Acked-by: Ben Pfaff <blp@ovn.org>