queue: Use discoverd to keep track of the workers.

We cannot use PIDs to check inactivity due to the way database/sql maintains a
pool of connections. Instead, we register the jobs in discoverd, and with a
uuid, and then unlock jobs locked by workers which don't appear in discoverd.

Signed-off-by: Blaž Hrastnik <blaz.hrast@gmail.com>
all: Add johto/notifyutils to dependencies.

Signed-off-by: Blaž Hrastnik <blaz.hrast@gmail.com>
WIP queue to use notifydispatcher

Signed-off-by: Blaž Hrastnik <blaz.hrast@gmail.com>