Enh: Maintenance checks

[geektophe]

This patch introduces maintenance checks, and extends the commands scheduling with check variants: it allows to have commands executed by pollers, but for other purpose than state check.

The maintenance check is an extension of the maintenance period, where maintenance state is got from a command return code (as a of state check) rather than a fixed predefined timeperiod. This allows to dynamically get and host or service maintenance state from an arbitrary command. This
command can for instance query the state in an external database or API.

Example:

define service {
    use                           generic-service
    host_name                     lb
    service_description           Web frontend
    check_command                 check_http_frontend
    maintenance_checks_enabled    1
    maintenance_check_command     check_release
    maintenance_check_interval    1
    maintenance_retry_interval    1
    maintenance_check_period      24x7
    ...
}

define command {
    command_name                  check_release
    command_line                  $PLUGINSDIR$/check_release_api
}

[coveralls]

Coverage increased (+0.01%) to 27.736% when pulling e78e8d9 on geektophe:enh_maintenance_checks into 0dfa784 on naparuba:master.

[naparuba]

Seems legit and useful.

I'll have a look at the code to see which part it can add complexity, but even with a little complexity+ should be ok, as maintaince as commands can be a really useful feature 👍

[olivierHa]

Nice feature !
@naparuba ok for merge on your side ?

[coveralls]

Coverage increased (+0.01%) to 27.737% when pulling c0c7cb2 on geektophe:enh_maintenance_checks into c64f2e4 on naparuba:master.

[geektophe]

Any news, is it OK for merging ?

[geektophe]

Still no news ?

[geektophe]

@naparuba did you have time to have a look at this PR ?

[geektophe]

@naparuba @olivierHa This patch works with success on my production platform for months, now.

I have a bug fix PR to push, and some lines interleave with this one. I'd really like to know If I have to publish it against the current master, or if this PR could be merged before.

Ideally, I'd prefer to avoid having to re-merge changes too often...

Thanks in advance.

[naparuba]

Very thanks for this patch, it's a very smart idea to export maintenance like this :)