Perfdata writers: disconnect handlers from signals in Pause()

[Al2Klimov]

as they would be re-connected in Resume() (HA).

Before they were still connected during pause and connected X+1 times
after X split-brains (the same data was written X+1 times).

[Al2Klimov]

Didn't backport to 2.12 for the same reason as you didn’t backport #9207.

[julianbrost]

after X split-brains

Not necessarily, just restarting one node is enough.

But note that this change only has an effect with enable_ha explicitly set to true (default is false), otherwise Resume() shouldn't be called multiple times anyways.

I did the following test:

• Set enable_ha = true on both my masters (in my setup, this cause only master-2 to write to InfluxDB)
• Stop master-2 (and wait until master-1 takes over writing to InfluxDB)
• Start master-2 (and wait for it to take over again)
• Repeat the previous steps a few times (to call Resume() a few times on master-1)
• Stop master-2 one last time so that master-1 takes over again
• Observe the InfluxDB queue item rate

Interpretation of the graph: Both lines show the item rate from Influxdb2Writer (influxdb2writer_influxdb-v2_work_queue_item_rate from the icinga check command, blue is master-1, purple is master-2). Events:

1. enable_ha = false, both masters are writing about 8 items/sec.
2. enable_ha = true is set. Now only one master writes about 8 items/sec.
3. Repeated starting and stopping of master-2 with current master branch: after this, when only master-1 is running, the rate goes up to around 45 items/sec.
4. (In addition to the steps mentioned above) Starting master-2 again so that it takes over again, its rate again is around 8 items/sec as on this instance, Resume() wasn't called multiple times.
5. Repeating the test with this PR, item rate stays at around 8 items/sec.

There are two instants where master-2 show a rather high item rate. But keep in mind that this node was restarted repeatedly and while it was gone, replay log accumulated that is handled when it's started, so a higher rate is expected for a short time.