ovsdb-client: Make "monitor" command able to monitor all tables.

Users may find this feature useful, but the reason to add this feature is
to allow a test to use it in an upcoming commit.

Signed-off-by: Ben Pfaff <blp@nicira.com>
jsonrpc-server: Add test for disconnecting connections with too long queues.

Signed-off-by: Ben Pfaff <blp@nicira.com>