Clean up child processes more reliably

The current code didn't seem to clean up children on exit. Also,
if there were no children to kill, the following error message
showed up on the console:
./snc.sh: line 1: jobs: unbound variable

This fixes both things by:
- replacing TERM with EXIT
- adding a check that 'jobs' is defined before trying to use it

snc.sh

@@ -9,7 +9,7 @@ source tools.sh
 source snc-library.sh
 
 # kill all the child processes for this script when it exits
-trap 'jobs=($(jobs -p)); ((${#jobs})) && kill "${jobs[@]}" || true; exit 0' TERM
+trap 'jobs=($(jobs -p)); [ -n "${jobs-}" ] && ((${#jobs})) && kill "${jobs[@]}" || true; exit 0' EXIT
 
 # If the user set OKD_VERSION in the environment, then use it to override OPENSHIFT_VERSION, MIRROR, and OPENSHIFT_INSTALL_RELEASE_IMAGE_OVERRIDE
 # Unless, those variables are explicitly set as well.