main: move install_crash_handler() and mount_cgroup_controllers() invocations

main: move install_crash_handler() and mount_cgroup_controllers() invocations

Let's place them in initialize_runtime(), where they appear to fit best.
Effectively this is just a move a little bit down, swapping places with
log_execution_mode(), which should require neither call to be done
first.

Note that changes the conditionalization a bit for these calls, from
(PID == 1) to (arg_system && arg_action == ACTION_RUN). At this point this is pretty much the same
however, as we don't allow PID 1 without ACTION_RUN and without
arg_system set, safety_checks() ensures that.