mysql-shun_recovery_time_sec not reliable when there's not traffic to the host group

[impimp]

Hello,

mysql-shun_recovery_time_sec has a nice notice of:

Note that if ProxySQL isn’t handling client traffic, there is no actual hard guarantee of the exact timing, but in practice it shouldn’t exceed this value by more than a couple of seconds.

I believe that a couple of seconds is weird but acceptable, although I'm afraid in reality there are cases in which it could be extremely long.

ProxySQL version: 2.2.0-percona-1.1, running on RHEL7. Steps to reproduce:

1. Create two hostgroups with some instances. It's important one node (let's call it X), is added to the both host groups.
2. Add some latency to the X node, for instance

tc qdisc add dev enp0s8 root netem delay 10001ms

3. After the node is shunned, remove the latency.

The node will remain as shunned forever. It will be correctly set to ONLINE after any client will reach a host group.