Update pbs-aprun launcher to use place/select for pbspro

The mpp* options have been deprecated (but still functional) for a while. Many
systems are completely disabling the mpp* options so we need to adjust to use
the place/select options for pbspro. For moab/torque we already used a different
set of options to request resources.
It looks like the other branches of the switch use one snprintf for all the -l options. Is there an advantage (or disadvantage) to splitting it up, besides code clarity?

(I don't know enough about this code to know one way or the other, so this is more education for me than anything.)