icinga - partly revert logfile permission fix

change I33f4f52f94aae0f1 puppetized icinga
logfile permission fixes but also changed this:

File[/var/log/icinga]/mode: mode changed '2757' to '2755'

reverting that change so it is like it was before

the cgi scripts running on Apache cant write to this directory
anymore, so things we do in the web ui don't show up anymore
in IRC, and also since this i have not seen a single other update
in this log, so i suspect it's even written to by yet another user

Change-Id: Ia83b9f7338e22301048a79a5a2176513349153eb
Merge "icinga - partly revert logfile permission fix" into production