WIP: Use 'nightly' instead of 'nightly_version' for RPM var

It's less typing.
12 jobs for dev-version-numbers in 30 minutes and 46 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Level0
passed #38014
level0:lal

00:05:22

 
  Level1
passed #38015
level1:lalframe

00:02:22

passed #38016
level1:lalmetaio

00:02:07

passed #38017
level1:lalsimulation

00:05:53

passed #38018
level1:lalxml

00:01:55

 
  Level2
passed #38019
level2:lalburst

00:02:25

passed #38020
level2:lalinspiral

00:05:33

passed #38021
level2:lalpulsar

00:03:57

passed #38022
level2:lalstochastic

00:02:16

 
  Level3
passed #38023
level3:laldetchar

00:02:23

passed #38024
level3:lalinference

00:07:15

 
  Level4
passed #38025
level4:lalapps

00:06:39