Changes

ansible: allow jenkins users to set rtprio 30

Create an /etc/security/limits.d file to allow the jenkins user to set
rtprio 30. This is required for running the ttcn3 bts testsuite through
testenv, as (unlike the previous approach with docker containers)
osmo-bts-trx runs without root rights there.

Change-Id: Id79851b3e3a47d19773aa9bba134b9bf99dbecbb