Add drain option to haproxy-endpoint-manage

Drain option allows to wait until all connections will close and then
move backend to the MAINT state. Task will wait until MAINT is reached,
so drain is disabled by default.

Change-Id: I531f2def83df9779f656ccb308d9b234f110107a

playbooks/common-tasks/haproxy-endpoint-manage.yml

@@ -17,6 +17,7 @@
   community.general.haproxy:
     socket: /var/run/haproxy.stat
     backend: "{{ haproxy_backend | default(omit) }}"
+    drain: "{{ haproxy_drain | default(False) }}"
     host: "{{ inventory_hostname }}"
     state: "{{ haproxy_state | default('enabled') }}"
     shutdown_sessions: "{{ haproxy_shutdown_sessions | default(False) | bool }}"