fix executable permission issue of python analysis scripts for post-processing

[nikizadehgfdl]

When an experiment starts on gaea the whole mom6/ directory (minus .datasets) is g-copied to gfdl /nbhome/$USER for PP.
But gcp does not preserve the (x-) permissions of the files. Hence when analysis scripts are called we get a permissions error like this:

/nbhome/Bonnie.Samuels/ulm_vanilla_dev_awg_mom6_2015.04.20/CM4_c96L48_am4f4_2000/mom6/tools/analysis/EddyKineticEnergy.py -g 00050101.ocean_static.nc -o /nbhome/Bonnie.Samuels/ulm_vanilla_dev_awg_mom6_2015.04.20/CM4_c96L48_am4f4_2000/refineDiag_ocean_annual/ocean_00050101/EddyKineticEnergy -l 00050101 00050101.ocean_daily.nc
/nbhome/Bonnie.Samuels/ulm_vanilla_dev_awg_mom6_2015.04.20/CM4_c96L48_am4f4_2000/mom6/tools/analysis/EddyKineticEnergy.py: Permission denied.

I suggest to add a "python " keyword before calling a python script in any caller shell script to avoid this.
The list of existing caller scripts is:
mom6/tools/analysis/MOM6_refineDiag.csh
mom6/ice_ocean_SIS/OM4_025/ocn_annual.frepp
mom6/ice_ocean_SIS/OM4_025/ocn_annual_z.frepp
mom6/ice_ocean_SIS/OM4_025/ocn_monthly.frepp

The workaround to this issue before it is solved is to do the following as part of the pp.starter (this is how the issue is currently avoided)
chmod -R +x mom6/

[adcroft]

Having just closed #4, the suggestions made there would fix this issue?