Allow to call a custom script from pfupdate to handle VIP in cloud environments

[nqb]

Description

• Call a custom script (outside PF tree), if it exists, each time keepalived is restarted or detected a change
• pfupdate will receive (as an argument) VIP of VRRP instance(s) when called

Custom script must be executable. Default location is /usr/local/bin/pfupdate-packetfence.sh. Script is not provided by default.

Impacts

• keepalived configuration
• pfupdate call

Issue

fixes #6657

Delete branch after merge

YES

NEWS file entries

Enhancements

• Allow to call a custom script from pfupdate to handle VIP in cloud environments

[nqb]

Changes done.

Could you review @satkunas and @fdurand ?

Thanks.