Decrease TCP retries in case of VIP failover

In case of VIP failover some connections (like mysql) can stuck
in retrying to connect and detect a dead connection. We
should probably make this failover to be detected faster then the
default value as suggested in [1]

[1] https://access.redhat.com/solutions/726753

Change-Id: Ia51f7f8f5225c4e350760093686858eabb3fec8a
Related-Bug: #1917068

releasenotes/notes/tcp_retries-bf32bab6e50fa97a.yaml

@@ -0,0 +1,9 @@
+---
+features:
+  - |
+    Added variable ``keepalived_sysctl_tcp_retries`` that allows to control
+    number of retries kernel will make to give up on connection. It controls
+    net.ipv4.tcp_retries2 sysctl setting which default value of which is 15.
+    Default value of ``keepalived_sysctl_tcp_retries`` is 8, so VIP failover
+    time will be ~1min. Setting ``keepalived_sysctl_tcp_retries`` to 0 will
+    remove mentioned sysctl setting.

tasks/main.yml

@@ -74,6 +74,15 @@
   tags:
     - openstack_hosts-install
 
+- name: Decreasing tcp_retries2 sysctl
+  sysctl:
+    name: "net.ipv4.tcp_retries2"
+    value: "{{ keepalived_sysctl_tcp_retries | default(8) }}"
+    sysctl_set: yes
+    state: "{{ (keepalived_sysctl_tcp_retries | default(8) > 0) | ternary('present', 'absent') }}"
+    reload: yes
+  failed_when: false
+
 - name: Install distro packages
   package:
     name: "{{ openstack_host_distro_packages }}"