icinga: use ssl_ciphersuite

make icinga use ssl_ciphersuite to
use our global SSL settings like most
other services. i'm slightly confused this wasn't
already done. i really thought i had. maybe there
was an issue with an earlier attempt?

Change-Id: I31e1232a043e3fc42c0f0fbb394efb10b44950b5
Merge "icinga: use ssl_ciphersuite" into production