Added idle_timelimit to nslcd

There is some bug in nslcd in CentOS6 which causes broking TCP LDAP connections few hours after restarting nslcd.

One workaround is to set idle_timelimit to lower value than default 3600 seconds. 

( the bug is mentioned here https://access.redhat.com/solutions/62655 without solution,
  leak of solution on https://access.redhat.com/solutions/458013,
  Debian version of bug https://bugs.launchpad.net/ubuntu/+source/nss-pam-ldapd/+bug/1074213 )

I've found other confirmations of the bug, but I'm not able to find them now.

Patch has been tested on Vagrant boxen for several hours without problems.