Add a way to set the open files limit in systemd service

[bigon]

Hello,

The sysconfig file contains a variable (MAXOPENFILES) that is used to set the limit for the opened files.

The problem is that under RHEL7, the hard limit set by systemd is 4096, that means that nothing can change that value to an higher value.

The .service file should be modified to allow setting this to an higher value (with probably the same default as the one in sysconfig, 8192)

[ekohl]

Since 98f46ca you can use a systemd::dropin_file for this. We no longer manage the service file itself (since packaging ships that). Perhaps this part could be enhanced as well if there's a need for this:

puppet-jenkins/manifests/config.pp

Lines 13 to 16 in f786482

	systemd::dropin_file { 'puppet-overrides.conf':
	unit => 'jenkins.service',
	content => epp("${module_name}/jenkins-override.epp", { 'environment' => $config_hash }),
	}